diff --git a/CHANGELOG.md b/CHANGELOG.md
index 79845fe..a7e0fc4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,37 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [2.0.0] - 2025-02-06
+
+### Breaking Changes
+
+- **`get_at` now raises `PathError` by default** for missing paths instead of returning `None` silently. Use the `default` parameter for optional/nullable access: `get_at(data, "path", default=None)`
+- **`get_at` and `set_at` parameters are now keyword-only** - The `default` and `create` parameters must be passed as keyword arguments (e.g., `get_at(data, "path", default=None)`, not `get_at(data, "path", None)`)
+- **`set_at` parameter change** - The `fill_strategy` parameter has been replaced with a simpler `create` boolean parameter. Replace `fill_strategy=FillStrategy.AUTO` with `create=True`
+- **No more sparse lists** - `set_at` no longer allows creating lists with gaps. Lists must be built sequentially (index 0, then 1, then 2, etc.). Attempting to set at index > len(list) raises `PathError`
+- **Removed `FillStrategy` enum** - Use `create=True/False` instead
+- **Implicit `None` returns from `get_at`** - Now raises `PathError` by default instead of returning `None` silently
+
+### Added
+
+- **Introspection module** with new functions for analyzing nested structures:
+  - `get_depth(data)` - Returns maximum nesting depth
+  - `count_leaves(data)` - Counts total leaf values
+  - `get_all_paths(data)` - Returns all paths to leaf values
+- **`default` parameter for `get_at`** - Explicit way to handle missing paths: `get_at(data, "path", default="fallback")`
+- **`create` parameter for `set_at`** - Simple boolean to control auto-creation of intermediate containers
+- **New error codes**:
+  - `OPERATION_DISABLED` - For operations blocked by configuration (e.g., list deletion without `allow_list_mutation=True`)
+  - `NON_NAVIGABLE_TYPE` - For attempts to navigate into non-container types (e.g., int, str, set)
+
+### Changed
+
+- Improved error messages with more context about what went wrong and how to fix it
+- Refactored internal helpers for better maintainability and testability
+- Enhanced path validation with clearer error codes
+
+For detailed migration instructions, see the [Migration Guide](https://ysskrishna.github.io/nestedutils/migration-v1-to-v2/).
+
 ## [1.1.7]
 
 ### Added
@@ -13,7 +44,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Radio button selection for three example datasets (User Profile, E-commerce Data, API Response) and custom JSON input
 - Consolidated path validation tests into `test_normalize_path.py` with new test cases for complex keys and None value handling
 
-
 ### Fixed
 
 - Fixed `normalize_path()` converting all list path keys to strings, now preserves integer and other key types.
@@ -133,6 +163,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Immutable container protection (tuples cannot be modified)
 - Safe list deletion (requires explicit `allow_list_mutation=True` flag)
 
+[2.0.0]: https://github.com/ysskrishna/nestedutils/compare/v1.1.7...v2.0.0
 [1.1.7]: https://github.com/ysskrishna/nestedutils/compare/v1.1.6...v1.1.7
 [1.1.6]: https://github.com/ysskrishna/nestedutils/compare/v1.1.5...v1.1.6
 [1.1.5]: https://github.com/ysskrishna/nestedutils/compare/v1.1.4...v1.1.5
diff --git a/README.md b/README.md
index 0b0ee36..56f0bae 100644
--- a/README.md
+++ b/README.md
@@ -37,8 +37,8 @@ user_name = get_at(data, "users.0.profile.name")
 - **Simple Path Syntax**: Use dot-notation strings (`"a.b.c"`) or lists (`["a", "b", "c"]`) to navigate nested structures
 - **Mixed Data Types**: Seamlessly work with dictionaries, lists, and tuples (read-only for tuples)
 - **List Index Support**: Access list elements using numeric indices, including negative indices
-- **Auto-creation**: Automatically create missing intermediate containers when setting values
-- **Flexible Fill Strategies**: Control how missing containers are created with different fill strategies
+- **Auto-creation**: Automatically create missing intermediate containers when setting values (with `create=True`)
+- **Introspection**: Analyze nested structures with `get_depth`, `count_leaves`, and `get_all_paths`
 - **Type Safety**: Comprehensive error handling with descriptive error messages and error codes
 - **Safety Limits**: Built-in protection against excessive nesting (max depth: 100) and oversized lists (max index: 10,000)
 - **Zero Dependencies**: Pure Python implementation with no external dependencies
@@ -49,6 +49,14 @@ user_name = get_at(data, "users.0.profile.name")
 - **Configuration Management**: Easily read and modify deeply nested settings in configuration dictionaries.
 - **Data Transformation**: Rapidly remap data from one complex structure to another using `get_at` and `set_at`.
 
+## Terminology
+
+| Term | Definition |
+|------|------------|
+| **Path** | A navigation string or list that specifies a location in nested data (e.g., `"user.profile.name"` or `["user", "profile", "name"]`) |
+| **Key** | An individual dictionary key used to access a value (e.g., `"name"`, `"profile"`) |
+| **Index** | A numeric position in a list or tuple (e.g., `0`, `-1` for last element) |
+
 ## Installation
 
 ```bash
@@ -58,16 +66,16 @@ pip install nestedutils
 ## Quick Start
 
 ```python
-from nestedutils import get_at, set_at, delete_at, exists_at
+from nestedutils import get_at, set_at, delete_at, exists_at, get_depth, count_leaves, get_all_paths
 
 # Create a nested structure
 data = {}
 
 # Set values using dot-notation
-set_at(data, "user.name", "John")
-set_at(data, "user.age", 30)
-set_at(data, "user.hobbies.0", "reading")
-set_at(data, "user.hobbies.1", "coding")
+set_at(data, "user.name", "John", create=True)
+set_at(data, "user.age", 30, create=True)
+set_at(data, "user.hobbies.0", "reading", create=True)
+set_at(data, "user.hobbies.1", "coding", create=True)
 
 # Access values
 name = get_at(data, "user.name")  # "John"
@@ -84,7 +92,7 @@ delete_at(data, "user.age")
 
 ## API Reference
 
-### `get_at(data, path, default=None)`
+### `get_at(data, path, *, default=None)`
 
 Retrieve a value from a nested data structure.
 
@@ -92,58 +100,67 @@ Retrieve a value from a nested data structure.
 
 - `data`: The data structure to navigate (dict, list, tuple, or nested combinations)
 - `path`: Path to the value (string with dot notation or list of keys/indices)
-- `default`: Value to return if path doesn't exist (default: `None`)
+- `default`: Value to return if path doesn't exist (keyword-only parameter, default: `None`)
+
+**Returns:** The value at the path, or `default` if provided and path doesn't exist
 
-**Returns:** The value at the path, or `default` if not found
+**Raises:** `PathError` if the path doesn't exist and `default` is not provided
+
+**Note:** By default, `get_at` raises `PathError` for missing paths. Use the `default` parameter for optional/nullable access.
 
 **Examples:**
 
 ```python
 data = {"a": {"b": {"c": 5}}}
 get_at(data, "a.b.c")  # 5
-get_at(data, "a.b.d", default=99)  # 99
+get_at(data, "a.b.d")  # Raises PathError (path doesn't exist)
+get_at(data, "a.b.d", default=99)  # 99 (returns default)
 
 data = {"items": [{"name": "apple"}, {"name": "banana"}]}
 get_at(data, "items.1.name")  # "banana"
 get_at(data, "items.-1.name")  # "banana" (negative index)
 ```
 
-### `set_at(data, path, value, fill_strategy="auto")`
+### `set_at(data, path, value, *, create=False)`
 
-Set a value in a nested data structure, creating intermediate containers as needed.
+Set a value in a nested data structure, optionally creating intermediate containers as needed.
 
 **Parameters:**
 
 - `data`: The data structure to modify (must be mutable: dict or list)
 - `path`: Path where to set the value (string with dot notation or list of keys/indices)
 - `value`: The value to set
-- `fill_strategy`: How to fill missing containers (default: `"auto"`)
-  - `"auto"`: Intelligently creates `{}` for dict keys, `[]` for list indices, and `None` for sparse list gaps
-  - `"none"`: Fills missing list items with `None`
-  - `"dict"`: Always creates dictionaries
-  - `"list"`: Always creates lists
+- `create`: If `True`, automatically creates missing intermediate containers (default: `False`)
 
-**Note:** Positive indices can extend lists (filling gaps as needed), but negative indices can only modify existing elements.
+**Note:** 
+- By default (`create=False`), `set_at` raises `PathError` if any intermediate key is missing
+- With `create=True`, missing containers are automatically created: `{}` for dict keys, `[]` for list indices
+- Positive indices can append to lists (index == len(list)) but cannot create gaps (index > len(list))
+- Negative indices can only modify existing elements
 
 **Examples:**
 
 ```python
+# create=True - auto-create missing containers
 data = {}
-set_at(data, "user.profile.name", "Alice")
+set_at(data, "user.profile.name", "Alice", create=True)
 # Creates: {"user": {"profile": {"name": "Alice"}}}
 
 data = {}
-set_at(data, "items.0.name", "Item 1")
+set_at(data, "items.0.name", "Item 1", create=True)
 # Creates: {"items": [{"name": "Item 1"}]}
 
+# Sequential list appending (no gaps allowed)
 data = {}
-set_at(data, "items.5", "Item 6", fill_strategy="none")
-# Creates: {"items": [None, None, None, None, None, "Item 6"]}
+set_at(data, "items.0", "first", create=True)  # Creates list with first item
+set_at(data, "items.1", "second", create=True)  # Appends second item
+# Creates: {"items": ["first", "second"]}
 
+# Sparse lists are NOT allowed - this raises PathError
 data = [1, 2, 3]
-set_at(data, "5", 99)  # Extends list with None gaps
-# Creates: [1, 2, 3, None, None, 99]
+set_at(data, "5", 99, create=True)  # Raises PathError: cannot create gap
 
+# Negative indices - modify existing only
 data = [1, 2, 3]
 set_at(data, "-1", 100)  # Updates existing last element
 # Creates: [1, 2, 100]
@@ -185,6 +202,8 @@ Delete a value from a nested data structure.
 - `path`: Path to the value to delete
 - `allow_list_mutation`: If `True`, allows deletion from lists (default: `False`)
 
+**Note:** List deletion is disabled by default to prevent accidental index shifting that could break subsequent code. When you delete an element from a list, all following indices shift down, which can cause unexpected behavior if other parts of your code reference those indices.
+
 **Returns:** The deleted value
 
 **Raises:** `PathError` if the path doesn't exist or deletion is not allowed
@@ -200,6 +219,79 @@ delete_at(data, "items.1", allow_list_mutation=True)  # Returns 2
 # data becomes {"items": [1, 3]}
 ```
 
+### `get_depth(data)`
+
+Get the maximum nesting depth of a data structure.
+
+**Parameters:**
+
+- `data`: Any nested structure (dict, list, tuple, or primitive)
+
+**Returns:** Integer depth. Primitives return 0, empty containers return 1.
+
+**Note:** Only dict, list, and tuple are traversed. Other container types (set, frozenset, etc.) are treated as leaf values.
+
+**Examples:**
+
+```python
+get_depth(42)                          # 0 (primitive)
+get_depth({})                          # 1 (empty container)
+get_depth({"a": 1})                    # 1 (flat dict)
+get_depth({"a": {"b": 1}})             # 2 (nested)
+get_depth({"a": {"b": {"c": 1}}})      # 3 (deeper nesting)
+get_depth([1, [2, [3]]])               # 3 (nested lists)
+```
+
+### `count_leaves(data)`
+
+Count the total number of leaf values (non-container values) in a nested structure.
+
+**Parameters:**
+
+- `data`: Any nested structure
+
+**Returns:** Integer count of leaf values. Empty containers return 0.
+
+**Note:** Only dict, list, and tuple are traversed. Other container types (set, frozenset, etc.) count as a single leaf.
+
+**Examples:**
+
+```python
+count_leaves(42)                       # 1 (primitive is a leaf)
+count_leaves({})                       # 0 (empty container)
+count_leaves({"a": 1, "b": 2})         # 2 (two leaf values)
+count_leaves({"a": {"b": 1, "c": 2}})  # 2 (nested, still 2 leaves)
+count_leaves([1, 2, [3, 4]])           # 4 (four leaf values)
+```
+
+### `get_all_paths(data)`
+
+Get all paths to leaf values in a nested structure.
+
+**Parameters:**
+
+- `data`: Any nested structure
+
+**Returns:** List of paths, where each path is a list of keys (strings) and indices (integers).
+
+**Note:** Only dict, list, and tuple are traversed. Other container types are treated as leaves.
+
+**Examples:**
+
+```python
+get_all_paths({"a": 1, "b": 2})
+# [["a"], ["b"]]
+
+get_all_paths({"a": {"b": 1, "c": 2}})
+# [["a", "b"], ["a", "c"]]
+
+get_all_paths({"users": [{"name": "Alice"}, {"name": "Bob"}]})
+# [["users", 0, "name"], ["users", 1, "name"]]
+
+get_all_paths({})                      # [] (no leaves)
+get_all_paths(42)                      # [[]] (primitive has empty path)
+```
+
 ## Error Handling
 
 The library uses `PathError` exceptions with error codes for different failure scenarios:
@@ -216,12 +308,15 @@ except PathError as e:
 
 **Error Codes:**
 
-- `INVALID_PATH`: Invalid path format or type
-- `INVALID_INDEX`: Invalid list index
-- `MISSING_KEY`: Key doesn't exist in dictionary
-- `EMPTY_PATH`: Path is empty
-- `IMMUTABLE_CONTAINER`: Attempted to modify a tuple
-- `INVALID_FILL_STRATEGY`: Invalid fill strategy value
+| Error Code | Description |
+|------------|-------------|
+| `INVALID_PATH` | Invalid path format or type |
+| `INVALID_INDEX` | Invalid list index |
+| `MISSING_KEY` | Key doesn't exist in dictionary |
+| `EMPTY_PATH` | Path is empty |
+| `IMMUTABLE_CONTAINER` | Attempted to modify a tuple |
+| `NON_NAVIGABLE_TYPE` | Attempted to navigate into a non-container type |
+| `OPERATION_DISABLED` | Operation is disabled by configuration (e.g., list deletion without `allow_list_mutation=True`) |
 
 ## Advanced Usage
 
@@ -231,8 +326,8 @@ List paths are useful when keys contain dots:
 
 ```python
 data = {}
-set_at(data, ["user.name", "first"], "John")
-set_at(data, ["user.name", "last"], "Doe")
+set_at(data, ["user.name", "first"], "John", create=True)
+set_at(data, ["user.name", "last"], "Doe", create=True)
 # Creates: {"user.name": {"first": "John", "last": "Doe"}}
 ```
 
@@ -272,19 +367,17 @@ set_at(data, "a.b.c", 10)
 
 The library includes built-in safety limits to prevent excessive resource usage:
 
-- **Maximum Path Depth**: 100 levels (prevents deeply nested paths that could cause stack issues)
-- **Maximum List Index**: 10,000 (prevents creating extremely large sparse lists)
+| Limit | Value | Description |
+|-------|-------|-------------|
+| **Maximum Path Depth** | 100 levels | Prevents deeply nested paths that could cause stack issues |
+| **Maximum List Index** | 10,000 | Prevents creating extremely large sparse lists |
 
 These limits help protect against accidental memory exhaustion or performance issues. If you hit these limits, you'll receive a `PathError` with a clear message.
 
 
-## Links
+## Migration from v1.x to v2.0
 
-- **PyPI**: [pypi.org/project/nestedutils](https://pypi.org/project/nestedutils/)
-- **Documentation**: [ysskrishna.github.io/nestedutils](https://ysskrishna.github.io/nestedutils/)
-- **Interactive Demo**: [ysskrishna.github.io/nestedutils/demo/](https://ysskrishna.github.io/nestedutils/demo/)
-- **Repository**: [github.com/ysskrishna/nestedutils.git](https://github.com/ysskrishna/nestedutils.git)
-- **Issues**: [github.com/ysskrishna/nestedutils/issues](https://github.com/ysskrishna/nestedutils/issues)
+Version 2.0 introduces breaking changes to make the library safer and more predictable. If you're upgrading from v1.x, please see the [Migration Guide](https://ysskrishna.github.io/nestedutils/migration-v1-to-v2/) for detailed upgrade instructions.
 
 ## Contributing
 
@@ -292,21 +385,25 @@ Contributions are welcome! Please read our [Contributing Guide](https://github.c
 
 ## Support
 
-If you find this library useful, please consider:
+If you find this library helpful:
 
-- ⭐ **Starring** the repository on GitHub to help others discover it.
-- 💖 **Sponsoring** to support ongoing maintenance and development.
-
-[Become a Sponsor on GitHub](https://github.com/sponsors/ysskrishna) | [Support on Patreon](https://patreon.com/ysskrishna)
+- ⭐ Star the repository
+- 🐛 Report issues
+- 🔀 Submit pull requests
+- 💝 [Sponsor on GitHub](https://github.com/sponsors/ysskrishna)
 
 ## License
 
-MIT License - see [LICENSE](https://github.com/ysskrishna/nestedutils/blob/main/LICENSE) file for details.
-
+MIT © [Y. Siva Sai Krishna](https://github.com/ysskrishna) - see [LICENSE](https://github.com/ysskrishna/nestedutils/blob/main/LICENSE) file for details.
 
-## Author
 
-**Y. Siva Sai Krishna**
+---
 
-- GitHub: [@ysskrishna](https://github.com/ysskrishna)
-- LinkedIn: [ysskrishna](https://linkedin.com/in/ysskrishna)
+<p align="left">
+  <a href="https://github.com/ysskrishna">Author's GitHub</a> •
+  <a href="https://linkedin.com/in/ysskrishna">Author's LinkedIn</a> •
+  <a href="https://github.com/ysskrishna/nestedutils/issues">Report Issues</a> •
+  <a href="https://pypi.org/project/nestedutils/">Package on PyPI</a> •
+  <a href="https://ysskrishna.github.io/nestedutils/">Package Documentation</a> •
+  <a href="https://ysskrishna.github.io/nestedutils/demo/">Package Demo</a>
+</p>
diff --git a/docs/api-reference.md b/docs/api-reference.md
index e7bccda..42a0da0 100644
--- a/docs/api-reference.md
+++ b/docs/api-reference.md
@@ -1,7 +1,7 @@
 ---
 title: API Reference
 
-description: "Complete API reference for nestedutils. Documentation for get_at, set_at, delete_at, and exists_at functions with parameters, return values, examples, and error handling."
+description: "Complete API reference for nestedutils. Documentation for get_at, set_at, delete_at, exists_at, get_depth, count_leaves, and get_all_paths functions with parameters, return values, examples, and error handling."
 
 keywords:
   - nestedutils API
@@ -10,6 +10,9 @@ keywords:
   - set_at
   - delete_at
   - exists_at
+  - get_depth
+  - count_leaves
+  - get_all_paths
   - function documentation
   - nested data functions
   - Python API
@@ -31,6 +34,16 @@ keywords:
         - exists_at
       heading_level: 3
 
+::: nestedutils.introspection
+    options:
+      show_root_heading: true
+      show_root_toc_entry: false
+      members:
+        - get_depth
+        - count_leaves
+        - get_all_paths
+      heading_level: 3
+
 ::: nestedutils.constants
     options:
       show_root_heading: true
@@ -48,7 +61,6 @@ keywords:
       heading_level: 3
       members:
         - PathErrorCode
-        - FillStrategy
       members_order: source
       show_if_no_docstring: true
 
diff --git a/docs/demo.md b/docs/demo.md
index 751b0ee..2180681 100644
--- a/docs/demo.md
+++ b/docs/demo.md
@@ -106,15 +106,10 @@ Try the `nestedutils` library directly in your browser! This page uses [Pyodide]
         placeholder="Value to set"
         style="flex: 1; min-width: 150px; padding: 8px; border: 1px solid #ccc; border-radius: 4px;"
       />
-      <select 
-        id="set-strategy" 
-        style="flex: 0 0 120px; padding: 8px; border: 1px solid #ccc; border-radius: 4px; background: white;"
-      >
-        <option value="auto">auto</option>
-        <option value="none">none</option>
-        <option value="dict">dict</option>
-        <option value="list">list</option>
-      </select>
+      <label style="display: flex; align-items: center; gap: 5px; padding: 8px; cursor: pointer;">
+        <input type="checkbox" id="set-create" checked />
+        <span style="font-size: 0.9em;">Create missing containers</span>
+      </label>
       <button 
         id="set-btn" 
         style="padding: 8px 16px; background: #1976d2; color: white; border: none; border-radius: 4px; cursor: pointer;"
@@ -123,8 +118,7 @@ Try the `nestedutils` library directly in your browser! This page uses [Pyodide]
       </button>
     </div>
     <p style="color: #666; font-size: 0.85em; margin-top: 5px;">
-      <strong>Fill Strategy:</strong> <code>auto</code> (smart defaults), <code>none</code> (fill gaps with None), 
-      <code>dict</code> (always create dicts), <code>list</code> (always create lists)
+      <strong>Create missing containers:</strong> When checked, automatically creates missing intermediate containers (dicts for string keys, lists for numeric keys).
     </p>
     <div id="set-result" style="margin-top: 10px; padding: 10px; background: #f5f5f5; border-radius: 4px; min-height: 30px;"></div>
   </div>
@@ -707,7 +701,7 @@ Try the `nestedutils` library directly in your browser! This page uses [Pyodide]
     document.getElementById("set-btn").addEventListener("click", async () => {
       const path = document.getElementById("set-path").value.trim();
       const value = document.getElementById("set-value").value.trim();
-      const strategy = document.getElementById("set-strategy").value;
+      const create = document.getElementById("set-create").checked;
       const resultDiv = document.getElementById("set-result");
       
       if (!path || value === "") {
@@ -738,7 +732,7 @@ Try the `nestedutils` library directly in your browser! This page uses [Pyodide]
           }
         }
         
-        pyodide.runPython(`set_at(data, ${JSON.stringify(path)}, ${JSON.stringify(parsedValue)}, fill_strategy=${JSON.stringify(strategy)})`);
+        pyodide.runPython(`set_at(data, ${JSON.stringify(path)}, ${JSON.stringify(parsedValue)}, create=${create ? 'True' : 'False'})`);
         updateDataDisplay(true);
         resultDiv.innerHTML = `<span class="result-success">✓ Value set successfully</span>`;
       } catch (error) {
diff --git a/docs/migration-v1-to-v2.md b/docs/migration-v1-to-v2.md
new file mode 100644
index 0000000..0c94c56
--- /dev/null
+++ b/docs/migration-v1-to-v2.md
@@ -0,0 +1,12 @@
+---
+title: Migration Guide - v1 to v2
+description: "Guide for migrating from nestedutils v1.x to v2.0. Covers breaking changes, API updates, and code migration examples."
+keywords:
+  - nestedutils
+  - migration
+  - upgrade guide
+  - v2
+  - breaking changes
+---
+
+--8<-- "migration-v1-to-v2.md"
diff --git a/migration-v1-to-v2.md b/migration-v1-to-v2.md
new file mode 100644
index 0000000..99579e4
--- /dev/null
+++ b/migration-v1-to-v2.md
@@ -0,0 +1,243 @@
+# Migration Guide: v1.x to v2.0
+
+This guide helps you upgrade your code from nestedutils v1.x to v2.0. Version 2.0 introduces breaking changes that make the library safer and more predictable.
+
+## Quick Summary of Breaking Changes
+
+| Change | v1.x Behavior | v2.0 Behavior |
+|--------|---------------|---------------|
+| `get_at` missing path | Returns `None` silently | Raises `PathError` |
+| `get_at` default parameter | Could be positional | Must be keyword-only (`default=...`) |
+| `set_at` auto-create | `fill_strategy` parameter | `create=False` parameter |
+| `set_at` create parameter | N/A (didn't exist) | Must be keyword-only (`create=...`) |
+| Sparse lists | Allowed with `None` fill | Not allowed (strict sequential) |
+| `FillStrategy` enum | Available | Removed |
+
+---
+
+## 1. `get_at` Now Raises by Default
+
+### The Change
+
+In v1.x, `get_at` silently returned `None` when a path didn't exist. In v2.0, it raises `PathError` by default, making missing data explicit rather than hidden.
+
+### v1.x Code
+
+```python
+from nestedutils import get_at
+
+data = {"user": {"name": "Alice"}}
+
+# v1.x: Returns None silently - bugs can hide here!
+email = get_at(data, "user.email")  # None
+age = get_at(data, "user.profile.age")  # None
+
+# v1.x: default could be passed positionally
+value = get_at(data, "missing.path", None)  # None (positional argument)
+```
+
+### v2.0 Migration
+
+**Option A: Use `default` parameter for optional values**
+
+```python
+from nestedutils import get_at
+
+data = {"user": {"name": "Alice"}}
+
+# Explicit default - clear intent
+email = get_at(data, "user.email", default=None)  # None
+email = get_at(data, "user.email", default="unknown@example.com")  # fallback value
+```
+
+**Option B: Use `exists_at` to check first**
+
+```python
+from nestedutils import get_at, exists_at
+
+if exists_at(data, "user.email"):
+    email = get_at(data, "user.email")
+else:
+    email = "default@example.com"
+```
+
+**Option C: Use try/except for error handling**
+
+```python
+from nestedutils import get_at, PathError
+
+try:
+    email = get_at(data, "user.email")
+except PathError:
+    email = "default@example.com"
+```
+
+### Why This Change?
+
+Silent `None` returns masked bugs. Consider:
+
+```python
+# v1.x - Bug hidden: typo in path returns None, not an error
+user_name = get_at(data, "usr.name")  # None (typo: "usr" vs "user")
+
+# v2.0 - Bug exposed immediately
+user_name = get_at(data, "usr.name")  # Raises PathError!
+```
+
+---
+
+## 2. `set_at` Parameter Changes
+
+### The Change
+
+The `fill_strategy` parameter has been replaced with a simpler `create` boolean parameter. Sparse list creation is no longer supported. **Important**: Both `get_at`'s `default` and `set_at`'s `create` are now keyword-only parameters (must use `default=...` and `create=...`, not positional arguments).
+
+### v1.x Code
+
+```python
+from nestedutils import set_at, FillStrategy
+
+data = {}
+
+# v1.x: Various fill strategies
+set_at(data, "user.name", "Alice", fill_strategy=FillStrategy.AUTO)
+set_at(data, "items.0", "first", fill_strategy=FillStrategy.AUTO)
+set_at(data, "items.5", "sixth", fill_strategy=FillStrategy.NONE)  # Sparse list!
+
+# v1.x: fill_strategy could be passed as string positionally
+set_at(data, "user.name", "Alice", "auto")  # Positional argument
+```
+
+### v2.0 Migration
+
+```python
+from nestedutils import set_at
+
+data = {}
+
+# v2.0: Simple create=True for auto-creation
+set_at(data, "user.name", "Alice", create=True)
+set_at(data, "items.0", "first", create=True)
+
+# Sparse lists are NO LONGER ALLOWED
+# set_at(data, "items.5", "sixth", create=True)  # Raises PathError!
+
+# Must build sequentially
+set_at(data, "items.1", "second", create=True)  # OK - appends
+```
+
+### FillStrategy Migration Table
+
+| v1.x `fill_strategy` | v2.0 Equivalent |
+|----------------------|-----------------|
+| `FillStrategy.AUTO` | `create=True` |
+| `FillStrategy.NONE` | Not supported (no sparse lists) |
+| `FillStrategy.DICT` | `create=True` (inferred from key type) |
+| `FillStrategy.LIST` | `create=True` (inferred from key type) |
+| Not specified | `create=False` (default, raises on missing) |
+
+### Why This Change?
+
+- Sparse lists (`[None, None, None, "value"]`) caused confusion and bugs
+- The `FillStrategy` enum added complexity without proportional benefit
+- `create=True/False` is more intuitive and covers most use cases
+
+---
+
+## 3. No More Sparse Lists
+
+### The Change
+
+v1.x allowed creating lists with gaps filled by `None`. v2.0 enforces sequential list building only.
+
+### v1.x Code
+
+```python
+from nestedutils import set_at
+
+data = {}
+set_at(data, "items.5", "value", fill_strategy=FillStrategy.NONE)
+# Result: {"items": [None, None, None, None, None, "value"]}
+```
+
+### v2.0 Migration
+
+```python
+from nestedutils import set_at
+
+data = {}
+
+# Build lists sequentially
+set_at(data, "items.0", "first", create=True)
+set_at(data, "items.1", "second", create=True)
+set_at(data, "items.2", "third", create=True)
+# Result: {"items": ["first", "second", "third"]}
+
+# Or use plain Python for sparse/pre-sized lists
+data = {"items": [None] * 6}
+set_at(data, "items.5", "value")  # OK - index exists
+```
+
+### Why This Change?
+
+Sparse lists often indicate logic errors. If you truly need sparse data, a dict with integer keys is more appropriate:
+
+```python
+# Instead of sparse list
+data = {"items": {5: "value", 10: "another"}}
+```
+
+---
+
+## 4. FillStrategy Enum Removed
+
+### The Change
+
+The `FillStrategy` enum has been removed from the public API.
+
+### v1.x Code
+
+```python
+from nestedutils import FillStrategy
+
+strategy = FillStrategy.AUTO
+```
+
+### v2.0 Migration
+
+Remove all `FillStrategy` imports and usages. Use `create=True/False` instead.
+
+```python
+# v2.0: No FillStrategy import needed
+from nestedutils import set_at
+
+set_at(data, "path", value, create=True)
+```
+
+---
+
+## 5. New Introspection Functions
+
+v2.0 adds new introspection functions that don't exist in v1.x:
+
+```python
+from nestedutils import get_depth, count_leaves, get_all_paths
+
+data = {"a": {"b": 1, "c": 2}, "d": [3, 4]}
+
+get_depth(data)       # 2
+count_leaves(data)    # 4
+get_all_paths(data)   # [["a", "b"], ["a", "c"], ["d", 0], ["d", 1]]
+```
+
+---
+
+## Migration Checklist
+
+- [ ] **Search for `get_at` calls without `default`** - Add `default=None` if silent failure is intended
+- [ ] **Update positional `default` arguments** - Change `get_at(data, "path", None)` to `get_at(data, "path", default=None)`
+- [ ] **Remove `FillStrategy` imports** - Replace with `create=True/False`
+- [ ] **Remove `fill_strategy` parameters** - Replace with `create=True`
+- [ ] **Update positional `fill_strategy` arguments** - Change `set_at(data, "path", value, "auto")` to `set_at(data, "path", value, create=True)`
+- [ ] **Check for sparse list creation** - Refactor to sequential building or use dicts
+- [ ] **Run your test suite** - v2.0's stricter behavior will expose hidden bugs
\ No newline at end of file
diff --git a/mkdocs.yml b/mkdocs.yml
index 53c86f4..7de55d2 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -13,6 +13,7 @@ nav:
   - Home: index.md
   - Interactive Demo: demo.md
   - API Reference: api-reference.md
+  - Migration Guide (v1 → v2): migration-v1-to-v2.md
   - Contributing: CONTRIBUTING.md
   - Changelog: CHANGELOG.md
   - License: LICENSE.md
diff --git a/nestedutils/__init__.py b/nestedutils/__init__.py
index 921c432..c515c4b 100644
--- a/nestedutils/__init__.py
+++ b/nestedutils/__init__.py
@@ -1,5 +1,21 @@
-from .access import get_at, set_at, delete_at, exists_at
-from .exceptions import PathError
-from .enums import PathErrorCode
+from nestedutils.access import get_at, set_at, delete_at, exists_at
+from nestedutils.introspection import get_depth, count_leaves, get_all_paths
+from nestedutils.exceptions import PathError
+from nestedutils.enums import PathErrorCode
 
-__all__ = ["get_at", "set_at", "delete_at", "exists_at", "PathError", "PathErrorCode"]
\ No newline at end of file
+__all__ = [
+    # Access
+    "get_at",
+    "set_at",
+    "delete_at",
+    "exists_at",
+
+    # Introspection
+    "get_depth",
+    "count_leaves",
+    "get_all_paths",
+
+    # Misc
+    "PathError",
+    "PathErrorCode",
+]
\ No newline at end of file
diff --git a/nestedutils/access.py b/nestedutils/access.py
index 5d65645..f2bf946 100644
--- a/nestedutils/access.py
+++ b/nestedutils/access.py
@@ -1,36 +1,50 @@
-from typing import Any, List, Literal, Union
-from .exceptions import PathError
-from .enums import PathErrorCode, FillStrategy
-from .helpers import normalize_path, navigate, create_container, fill_list_gaps, ensure_container_at_index
-from .helpers import is_int_key, resolve_write_index
+from typing import Any, List, Union
+from nestedutils.exceptions import PathError
+from nestedutils.enums import PathErrorCode
+from nestedutils.helpers import (
+    normalize_path,
+    navigate_one_step,
+    navigate_to_parent,
+    set_final_value,
+    navigate_to_parent_for_delete,
+    delete_from_container,
+    MISSING,
+)
 
 
-def get_at(data: Any, path: Union[str, List[Any]], default: Any = None) -> Any:
+def get_at(data: Any, path: Union[str, List[Any]], *, default: Any = MISSING) -> Any:
     """Retrieve a value from a nested data structure.
     
     Navigates through nested dictionaries, lists, and tuples using a path specified as either
-    a dot-notation string or a list of keys/indices. Returns ``default`` if the path does not
-    exist or an index is out of bounds (positive or negative). Supports negative indexing for
-    lists and tuples.
+    a dot-notation string or a list of keys/indices. By default, raises PathError if the path
+    does not exist. Use the `default` parameter to return a value instead of raising.
+    Supports negative indexing for lists and tuples.
     
     Args:
         data: The data structure to navigate (dict, list, tuple, or nested combinations).
         path: Path to the value. Accepts either a dot-separated string (e.g., "a.b.0.name") or
             a list of keys/indices (e.g., ["a", "b", 0, "name"]). Indices may be integers or
             strings representing integers (including negative indices).
-        default: Value to return if the path does not exist (default: None).
+        default: Value to return if the path does not exist. If not provided, raises PathError
+            for missing paths.
     
     Returns:
-        The value at the specified path, or ``default`` if the path does not exist.
+        The value at the specified path, or ``default`` if the path does not exist and
+        ``default`` is provided.
     
     Raises:
-        PathError: If the path is malformed, empty, or contains empty keys.
+        PathError: If the path is malformed, empty, contains empty keys, or path doesn't exist
+            (when default is not provided).
     
     Examples:
         ```python
         data = {"a": {"b": {"c": 5}}}
         get_at(data, "a.b.c")  # Returns: 5
         
+        # Missing paths raise by default
+        get_at(data, "a.b.d")  # Raises: PathError
+        
+        # Explicit default for optional values
         get_at(data, "a.b.d", default=99)  # Returns: 99
         
         data = {"items": [{"name": "apple"}, {"name": "banana"}]}
@@ -46,12 +60,14 @@ def get_at(data: Any, path: Union[str, List[Any]], default: Any = None) -> Any:
     """
     keys = normalize_path(path)
     current = data
-    MISSING = object()
     
     for key in keys:
-        current = navigate(current, key, MISSING)
-        if current is MISSING:
-            return default
+        current = navigate_one_step(
+            current,
+            key,
+            default=default,
+            raise_on_missing=(default is MISSING)
+        )
     
     return current
 
@@ -60,8 +76,11 @@ def exists_at(data: Any, path: Union[str, List[Any]]) -> bool:
     """Check if a path exists in a nested data structure.
     
     Navigates through nested dictionaries, lists, and tuples. Returns True if the full path
-    exists, False otherwise (including for any out-of-bounds index, positive or negative).
-    Supports negative indexing for lists and tuples.
+    exists and is accessible, False otherwise (including out-of-bounds indices). Supports
+    negative indexing for lists and tuples.
+    
+    This function never raises PathError for missing paths - it returns False instead.
+    PathError is only raised for malformed paths.
     
     Args:
         data: The data structure to navigate (dict, list, tuple, or nested combinations).
@@ -69,10 +88,10 @@ def exists_at(data: Any, path: Union[str, List[Any]]) -> bool:
             list of keys/indices (e.g., ["a", "b", 0, "name"]).
     
     Returns:
-        True if the path exists, False otherwise.
+        True if the path exists and is accessible, False otherwise.
     
     Raises:
-        PathError: If the path is malformed, empty, or contains empty keys.
+        PathError: Only if the path format is invalid (empty, malformed, exceeds max depth).
     
     Examples:
         ```python
@@ -89,163 +108,109 @@ def exists_at(data: Any, path: Union[str, List[Any]]) -> bool:
         data = (10, 20, 30)
         exists_at(data, "2")  # Returns: True
         exists_at(data, "5")  # Returns: False
+        
+        # Even None values return True if path exists
+        data = {"a": {"b": None}}
+        exists_at(data, "a.b")  # Returns: True
+        exists_at(data, "a.b.c")  # Returns: False (can't navigate into None)
         ```
     """
-    keys = normalize_path(path)
-    current = data
-    MISSING = object()
-    
-    for key in keys:
-        current = navigate(current, key, MISSING)
-        if current is MISSING:
+    try:
+        get_at(data, path)  # No default provided, so raises on missing path
+        return True
+    except PathError as e:
+        # Return False for "not found" errors or navigation into non-navigable types
+        if e.code in (PathErrorCode.MISSING_KEY, PathErrorCode.INVALID_INDEX, PathErrorCode.NON_NAVIGABLE_TYPE):
             return False
-    
-    return True
+        # Re-raise for path format errors and any other errors
+        raise
 
 
 def set_at(
     data: Any,
     path: Union[str, List[Any]],
     value: Any,
-    fill_strategy: Literal["auto", "none", "dict", "list"] = "auto"
+    *,
+    create: bool = False
 ) -> None:
-    """Set a value in a nested data structure, creating intermediate containers as needed.
+    """Set a value in a nested data structure.
     
-    Navigates to the specified path and sets the value, automatically creating missing
-    intermediate dictionaries or lists according to ``fill_strategy``.
+    Navigates to the specified path and sets the value. By default (create=False),
+    raises PathError if any intermediate key is missing. With create=True, automatically
+    creates missing intermediate containers (dicts for string keys, lists for numeric keys).
     
     List indexing rules:
-        - Non-negative indices can extend the list, filling gaps as needed.
-        - Negative indices can only modify existing elements (no extension allowed).
-        - Out-of-bounds negative indices raise PathError.
+    - Positive indices can append (index == len(list)) but NOT create gaps (index > len(list))
+    - Negative indices can only modify existing elements
+    - Out-of-bounds negative indices raise PathError
+    - Index cannot exceed MAX_LIST_SIZE (10000)
     
     Args:
-        data: The mutable data structure to modify (dict or list). Intermediate containers are
-            created automatically, but the root must be mutable.
+        data: The mutable data structure to modify (dict or list). The root container
+            must already exist and be mutable.
         path: Path where to set the value. Accepts either a dot-separated string (e.g., "a.b.0.name")
             or a list of keys/indices (e.g., ["a", "b", 0, "name"]).
         value: The value to set at the specified path.
-        fill_strategy: Controls how missing intermediate containers are created. Must be one of:
-            - 'auto' (default): creates {} for dict keys, [] for list indices, and None for sparse
-              list gaps.
-            - 'none': fills sparse list gaps with None.
-            - 'dict': always creates dictionaries {} for missing containers.
-            - 'list': always creates lists [] for missing containers.
+        create: If True, automatically create missing intermediate containers.
+            If False (default), raise PathError if path doesn't exist.
     
     Returns:
         None. The function modifies ``data`` in place.
     
     Raises:
-        PathError: If the path is malformed, empty, attempts to modify a tuple, uses an invalid
-            fill_strategy, or uses an out-of-bounds negative index.
-    
-    Note:
-        When extending lists with gaps (e.g., setting index 5 on a list of length 2),
-        intermediate positions are filled based on ``fill_strategy`` ('auto' and 'none' use None;
-        'dict' uses {}; 'list' uses []).
+        PathError: If path is malformed, path doesn't exist (when create=False),
+            attempts to modify tuple, uses out-of-bounds negative index, or would
+            create sparse list.
     
     Examples:
         ```python
-        data = {}
-        set_at(data, "user.profile.name", "Alice")
+        # create=False (default) - path must exist
+        data = {"user": {"profile": {}}}
+        set_at(data, "user.profile.name", "Alice")  # OK - path exists
         # data is now: {'user': {'profile': {'name': 'Alice'}}}
         
         data = {}
-        set_at(data, "items.0.name", "Item 1")
-        # data is now: {'items': [{'name': 'Item 1'}]}
+        set_at(data, "user.name", "Bob")  # PathError - path doesn't exist
         
+        # create=True - auto-create missing parts
         data = {}
-        set_at(data, "items.5", "last", fill_strategy="none")
-        # data is now: {'items': [None, None, None, None, None, 'last']}
+        set_at(data, "user.profile.name", "Alice", create=True)
+        # data is now: {'user': {'profile': {'name': 'Alice'}}}
         
+        # List operations - sequential only (no gaps)
         data = {}
-        set_at(data, "items.2.sub.value", 42)  # 'auto' creates dict at target index, None for gaps
-        # data is now: {'items': [None, None, {'sub': {'value': 42}}]}
+        set_at(data, "items.0", "first", create=True)  # OK - creates list
+        # data is now: {'items': ['first']}
         
-        data = [1, 2, 3]
-        set_at(data, "5", 99)  # extends with None gaps
-        # data is now: [1, 2, 3, None, None, 99]
-        
-        set_at(data, "-1", 100)  # modifies existing last element
-        # data is now: [1, 2, 3, None, None, 100]
-        ```
-    """
-    try:
-        strategy = FillStrategy(fill_strategy)
-    except ValueError:
-        valid = {s.value for s in FillStrategy}
-        raise PathError(
-            f"Invalid fill_strategy: {fill_strategy}. Valid: {valid}",
-            PathErrorCode.INVALID_FILL_STRATEGY
-        )
-    
-    keys = normalize_path(path)
-    current = data
-    
-    # Navigate intermediate keys
-    for i, key in enumerate(keys[:-1]):
-        next_key = keys[i + 1]
+        set_at(data, "items.1", "second", create=True)  # OK - appends
+        # data is now: {'items': ['first', 'second']}
         
-        if isinstance(current, dict):
-            if key not in current or current[key] is None:
-                current[key] = create_container(strategy, next_key)
-            current = current[key]
+        set_at(data, "items.5", "x", create=True)  # PathError - would create gap
         
-        elif isinstance(current, list):
-            if not is_int_key(key):
-                raise PathError(
-                    f"Expected numeric index, got '{key}'",
-                    PathErrorCode.INVALID_INDEX
-                )
-            
-            idx = resolve_write_index(current, key, allow_extension=True)
-            fill_list_gaps(current, idx, strategy)
-            ensure_container_at_index(current, idx, strategy, next_key)
-            current = current[idx]
-        
-        elif isinstance(current, tuple):
-            raise PathError(
-                "Cannot modify tuple (immutable)",
-                PathErrorCode.IMMUTABLE_CONTAINER
-            )
-        
-        else:
-            raise PathError(
-                f"Cannot navigate into {type(current).__name__}",
-                PathErrorCode.INVALID_PATH
-            )
-    
-    # Set final value
-    final_key = keys[-1]
-    
-    if isinstance(current, dict):
-        current[final_key] = value
-    
-    elif isinstance(current, list):
-        if not is_int_key(final_key):
-            raise PathError(
-                f"Expected numeric index, got '{final_key}'",
-                PathErrorCode.INVALID_INDEX
-            )
-        
-        idx = resolve_write_index(current, final_key, allow_extension=True)
+        # Negative indices - modify existing only
+        data = {"items": [1, 2, 3]}
+        set_at(data, "items.-1", 99)  # OK - modifies last element
+        # data is now: {'items': [1, 2, 99]}
         
-        while len(current) <= idx:
-            current.append(None)
+        set_at(data, "items.-5", 0)  # PathError - out of bounds
         
-        current[idx] = value
-    
-    elif isinstance(current, tuple):
-        raise PathError(
-            "Cannot modify tuple (immutable)",
-            PathErrorCode.IMMUTABLE_CONTAINER
-        )
+        # Modifying existing nested structures
+        data = {"a": [{"x": 1}]}
+        set_at(data, "a.0.y", 2, create=True)  # Adds key to existing dict
+        # data is now: {'a': [{'x': 1, 'y': 2}]}
+        ```
+    """
+    keys = normalize_path(path)
     
+    if len(keys) == 1:
+        # Single key - set directly on root
+        set_final_value(data, keys[0], value, create=create)
     else:
-        raise PathError(
-            f"Cannot set value in {type(current).__name__}",
-            PathErrorCode.INVALID_PATH
-        )
+        # Navigate to parent, then set final value
+        intermediate_keys = keys[:-1]
+        final_key = keys[-1]
+        parent = navigate_to_parent(data, intermediate_keys, final_key, create=create)
+        set_final_value(parent, final_key, value, create=create)
 
 
 def delete_at(
@@ -293,69 +258,13 @@ def delete_at(
         ```
     """
     keys = normalize_path(path)
-    current = data
-    
-    # Navigate to parent
-    for key in keys[:-1]:
-        if isinstance(current, dict):
-            if key not in current:
-                raise PathError(
-                    f"Key not found: '{key}'",
-                    PathErrorCode.MISSING_KEY
-                )
-            current = current[key]
-        
-        elif isinstance(current, (list, tuple)):
-            if not is_int_key(key):
-                raise PathError(
-                    f"Expected numeric index, got '{key}'",
-                    PathErrorCode.INVALID_INDEX
-                )
-            
-            idx = resolve_write_index(current, key, allow_extension=False)
-            current = current[idx]
-        
-        else:
-            raise PathError(
-                f"Cannot navigate through {type(current).__name__}",
-                PathErrorCode.INVALID_PATH
-            )
-    
-    # Delete final key
-    final_key = keys[-1]
-    
-    if isinstance(current, dict):
-        if final_key not in current:
-            raise PathError(
-                f"Key not found: '{final_key}'",
-                PathErrorCode.MISSING_KEY
-            )
-        return current.pop(final_key)
-    
-    elif isinstance(current, list):
-        if not allow_list_mutation:
-            raise PathError(
-                "List deletion disabled. Set allow_list_mutation=True",
-                PathErrorCode.INVALID_PATH
-            )
-        
-        if not is_int_key(final_key):
-            raise PathError(
-                f"Expected numeric index, got '{final_key}'",
-                PathErrorCode.INVALID_INDEX
-            )
-        
-        idx = resolve_write_index(current, final_key, allow_extension=False)
-        return current.pop(idx)
-    
-    elif isinstance(current, tuple):
-        raise PathError(
-            "Cannot delete from tuple (immutable)",
-            PathErrorCode.IMMUTABLE_CONTAINER
-        )
     
+    if len(keys) == 1:
+        # Single key - delete directly from root
+        return delete_from_container(data, keys[0], allow_list_mutation=allow_list_mutation)
     else:
-        raise PathError(
-            f"Cannot delete from {type(current).__name__}",
-            PathErrorCode.INVALID_PATH
-        )
\ No newline at end of file
+        # Navigate to parent, then delete final key
+        intermediate_keys = keys[:-1]
+        final_key = keys[-1]
+        parent = navigate_to_parent_for_delete(data, intermediate_keys)
+        return delete_from_container(parent, final_key, allow_list_mutation=allow_list_mutation)
\ No newline at end of file
diff --git a/nestedutils/enums.py b/nestedutils/enums.py
index 849dfa8..7517fa0 100644
--- a/nestedutils/enums.py
+++ b/nestedutils/enums.py
@@ -1,7 +1,7 @@
 """Enumerations for nestedutils library.
 
-This module defines error codes and configuration enums used throughout
-the nestedutils library for consistent error handling and behavior control.
+This module defines error codes used throughout the nestedutils library
+for consistent error handling.
 """
 
 from enum import Enum
@@ -16,32 +16,30 @@ class PathErrorCode(Enum):
         
         data = {"a": {"b": 1}}
         try:
-            get_at(data, "a.c.d")
+            result = get_at(data, "a.c.d")
+            # get_at raises PathError for missing paths in v2.0
         except PathError as e:
             if e.code == PathErrorCode.MISSING_KEY:
                 print("Key not found")
         ```
     """
     INVALID_INDEX = "INVALID_INDEX"
+    """Raised when a list index is invalid (non-numeric, out of bounds, or would create sparse list)."""
+    
     MISSING_KEY = "MISSING_KEY"
+    """Raised when a required key doesn't exist (in set_at with create=False or delete_at)."""
+    
     EMPTY_PATH = "EMPTY_PATH"
+    """Raised when path is empty or contains empty keys."""
+    
     IMMUTABLE_CONTAINER = "IMMUTABLE_CONTAINER"
+    """Raised when attempting to modify an immutable container (tuple)."""
+    
     INVALID_PATH = "INVALID_PATH"
-    INVALID_FILL_STRATEGY = "INVALID_FILL_STRATEGY"
-
-
-class FillStrategy(Enum):
-    """Strategy for filling missing containers when setting nested paths.
+    """Raised when path format is invalid (wrong type, exceeds max depth, etc.)."""
     
-    Example:
-        ```python
-        from nestedutils import set_at, FillStrategy
-        
-        data = {}
-        set_at(data, "items.0.name", "apple", fill_strategy=FillStrategy.AUTO)
-        ```
-    """
-    AUTO = "auto"
-    NONE = "none"
-    DICT = "dict"
-    LIST = "list"
\ No newline at end of file
+    NON_NAVIGABLE_TYPE = "NON_NAVIGABLE_TYPE"
+    """Raised when attempting to navigate into a non-container type (e.g., None, int, str)."""
+    
+    OPERATION_DISABLED = "OPERATION_DISABLED"
+    """Raised when an operation is disabled by configuration (e.g., list mutation without allow_list_mutation=True)."""
\ No newline at end of file
diff --git a/nestedutils/exceptions.py b/nestedutils/exceptions.py
index d177581..a5f5cd9 100644
--- a/nestedutils/exceptions.py
+++ b/nestedutils/exceptions.py
@@ -6,7 +6,7 @@
 """
 
 from typing import Optional
-from .enums import PathErrorCode
+from nestedutils.enums import PathErrorCode
 
 
 class PathError(Exception):
@@ -18,14 +18,21 @@ class PathError(Exception):
     
     Example:
         ```python
-        from nestedutils import get_at, PathError, PathErrorCode
+        from nestedutils import set_at, PathError, PathErrorCode
         
         data = {"a": {"b": 1}}
+        
+        # set_at raises when path doesn't exist (create=False is default)
         try:
-            get_at(data, "a.c.d")
+            set_at(data, "a.c.d", "value")
         except PathError as e:
             if e.code == PathErrorCode.MISSING_KEY:
-                print("Key not found")
+                print(f"Path doesn't exist: {e.message}")
+        
+        # get_at raises for missing paths in v2.0 - use default= for optional values
+        from nestedutils import get_at
+        result = get_at(data, "a.c.d", default="not found")
+        print(result)  # "not found"
         ```
     """
     
diff --git a/nestedutils/helpers.py b/nestedutils/helpers.py
index c881216..8da8e49 100644
--- a/nestedutils/helpers.py
+++ b/nestedutils/helpers.py
@@ -1,29 +1,48 @@
 from typing import Any, List, Union, Optional
-from .exceptions import PathError
-from .enums import PathErrorCode, FillStrategy
-from .constants import MAX_DEPTH, MAX_LIST_SIZE
+from nestedutils.exceptions import PathError
+from nestedutils.enums import PathErrorCode
+from nestedutils.constants import MAX_DEPTH, MAX_LIST_SIZE
 
 
-def normalize_path(path: Union[str, List[Any]]) -> List[str]:
-    """Normalize path to list of strings and validate.
+def normalize_path(path: Union[str, List[Any]]) -> List[Union[str, int]]:
+    """Normalize path to list of keys and validate.
     
-    Converts path to a list of string keys, validating that:
+    Converts path to a list of keys (strings or integers), validating that:
     - Path is not empty
     - No keys in the path are empty strings
     - Path depth does not exceed MAX_DEPTH
     
+    For list paths, integer types are preserved to support dictionary keys with integer keys.
+    For string paths (dot-notation), all keys are strings.
+    
     Args:
         path: Either a dot-notation string (e.g., "a.b.c") or a list of keys.
     
     Returns:
-        List of string keys representing the path.
+        List of keys representing the path. Elements may be strings or integers.
+        - String paths always return List[str]
+        - List paths preserve integer types: List[Union[str, int]]
     
     Raises:
         PathError: If path format is invalid, path is empty, contains empty keys,
             or exceeds maximum depth.
     """
     if isinstance(path, list):
-        keys = [key for key in path]
+        # Preserve integer types from list paths to support dict keys with integer keys
+        keys: List[Union[str, int]] = []
+        for key in path:
+            if isinstance(key, int):
+                keys.append(key)
+            elif isinstance(key, str):
+                if key == "":
+                    raise PathError("Path cannot contain empty keys", PathErrorCode.EMPTY_PATH)
+                keys.append(key)
+            else:
+                # Convert other types to strings (e.g., bool, float)
+                key_str = str(key)
+                if key_str == "":
+                    raise PathError("Path cannot contain empty keys", PathErrorCode.EMPTY_PATH)
+                keys.append(key_str)
     elif isinstance(path, str):
         keys = path.split(".")
     else:
@@ -41,31 +60,52 @@ def normalize_path(path: Union[str, List[Any]]) -> List[str]:
             PathErrorCode.INVALID_PATH
         )
     
-    if any(key == "" for key in keys):
+    # Check for empty strings (integers can't be empty)
+    if any(key == "" for key in keys if isinstance(key, str)):
         raise PathError("Path cannot contain empty keys", PathErrorCode.EMPTY_PATH)
     
     return keys
 
 
-def is_int_key(key: str) -> bool:
+def is_int_key(key: Union[str, int]) -> bool:
     """Check if a key represents a valid integer index.
     
+    Accepts both integer types and string representations of integers.
+    Rejects: bool, float, complex, or any other type.
+    
     Args:
-        key: String to check.
+        key: String or integer to check.
     
     Returns:
-        True if key can be parsed as an integer, False otherwise.
+        True if key is an integer or can be parsed as an integer, False otherwise.
     
     Examples:
         >>> is_int_key("0")
         True
         >>> is_int_key("-1")
         True
+        >>> is_int_key(0)
+        True
+        >>> is_int_key(-1)
+        True
         >>> is_int_key("abc")
         False
-        >>> is_int_key("-")
+        >>> is_int_key("")
+        False
+        >>> is_int_key(True)  # Not int or string
+        False
+        >>> is_int_key(3.14)  # Not int or string
         False
     """
+    if isinstance(key, int):
+        return True
+    
+    if not isinstance(key, str):
+        return False
+    
+    if not key:  # Empty string
+        return False
+    
     try:
         int(key)
         return True
@@ -73,25 +113,28 @@ def is_int_key(key: str) -> bool:
         return False
 
 
-def parse_int_key(key: str) -> int:
-    """Parse a string key into an integer index.
+def parse_int_key(key: Union[str, int]) -> int:
+    """Parse a key into an integer index.
     
     Args:
-        key: String representation of an index.
+        key: String representation of an index or an integer.
     
     Returns:
-        Parsed integer index.
+        Integer index.
     
     Raises:
-        PathError: If key cannot be parsed as an integer.
+        PathError: If key is a string that cannot be parsed as an integer.
     """
+    if isinstance(key, int):
+        return key
+    
     try:
         return int(key)
     except ValueError:
         raise PathError(f"Invalid list index: '{key}'", PathErrorCode.INVALID_INDEX)
 
 
-def resolve_read_index(container: Union[list, tuple], key: str) -> Optional[int]:
+def resolve_read_index(container: Union[list, tuple], key: Union[str, int]) -> Optional[int]:
     """Resolve index for read operations (get_at, exists_at).
     
     Read operations are graceful - out-of-bounds indices return None
@@ -99,7 +142,7 @@ def resolve_read_index(container: Union[list, tuple], key: str) -> Optional[int]
     
     Args:
         container: The list or tuple to index into.
-        key: String representation of the index.
+        key: String representation of the index or an integer.
     
     Returns:
         Resolved positive index, or None if out of bounds.
@@ -118,29 +161,52 @@ def resolve_read_index(container: Union[list, tuple], key: str) -> Optional[int]
     return None
 
 
-def resolve_write_index(container: list, key: str, allow_extension: bool = True) -> int:
+def resolve_write_index(container: list, key: Union[str, int]) -> int:
     """Resolve index for write operations (set_at).
     
-    Write operations have stricter semantics:
+    Write operations have strict semantics to prevent sparse lists:
     - Negative indices must reference existing elements (no extension)
-    - Positive indices can extend the list if allow_extension=True
-    - Positive indices cannot exceed MAX_LIST_SIZE to prevent memory exhaustion
+    - Positive indices can only extend by 1 (append operation)
+    - Index must be <= len(list) (can append, but not create gaps)
+    - Index cannot exceed MAX_LIST_SIZE
     
     Args:
         container: The list to index into.
-        key: String representation of the index.
-        allow_extension: If True, positive indices can exceed current list length.
-                        If False, all indices must reference existing elements.
+        key: String representation of the index or an integer.
     
     Returns:
         Resolved positive index.
     
     Raises:
-        PathError: If index is out of bounds, exceeds MAX_LIST_SIZE, or key cannot be parsed as integer.
+        PathError: If index is out of bounds, would create sparse list,
+            exceeds MAX_LIST_SIZE, or key is not a valid integer.
+    
+    Examples:
+        >>> lst = [10, 20, 30]
+        >>> resolve_write_index(lst, "3")  # Append
+        3
+        >>> resolve_write_index(lst, 3)  # Append (integer)
+        3
+        >>> resolve_write_index(lst, "1")  # Modify existing
+        1
+        >>> resolve_write_index(lst, "-1")  # Modify last
+        2
+        >>> resolve_write_index(lst, "5")  # Would create gap
+        PathError: Index 5 out of bounds for list of length 3 (no sparse lists)
+        >>> resolve_write_index(lst, "-5")  # Negative out of bounds
+        PathError: Index -5 out of bounds for list of length 3
     """
     idx = parse_int_key(key)
     length = len(container)
     
+    # Check maximum size limit first (before any calculations)
+    if idx > MAX_LIST_SIZE:
+        raise PathError(
+            f"List index {idx} exceeds maximum size {MAX_LIST_SIZE}",
+            PathErrorCode.INVALID_INDEX
+        )
+    
+    # Handle negative indices
     if idx < 0:
         resolved = length + idx
         if resolved < 0 or resolved >= length:
@@ -150,104 +216,427 @@ def resolve_write_index(container: list, key: str, allow_extension: bool = True)
             )
         return resolved
     
-    # Check maximum list size when extension is allowed
-    if allow_extension and idx > MAX_LIST_SIZE:
+    # Handle positive indices - NO SPARSE LISTS
+    if idx > length:
         raise PathError(
-            f"List index {idx} exceeds maximum size {MAX_LIST_SIZE}",
-            PathErrorCode.INVALID_INDEX
-        )
-    
-    if not allow_extension and idx >= length:
-        raise PathError(
-            f"Index {key} out of bounds for list of length {length}",
+            f"Index {idx} out of bounds for list of length {length} "
+            f"(no sparse lists allowed - index must be <= {length})",
             PathErrorCode.INVALID_INDEX
         )
     
     return idx
 
 
-def navigate(container: Any, key: str, default: Any) -> Any:
-    """Navigate one level into a container.
+def create_intermediate_container(next_key: Union[str, int]) -> Union[dict, list]:
+    """Create intermediate container based on next key type.
     
-    Used by read operations (get_at, exists_at). Returns default
-    for any navigation failures rather than raising exceptions.
+    Logic:
+    - If next_key is numeric (int or numeric string) → create list
+    - Otherwise → create dict
     
     Args:
-        container: Container to navigate into (dict, list, or tuple).
-        key: Key or index to access.
-        default: Sentinel value to return on failure.
+        next_key: The next key in the path (string or integer).
     
     Returns:
-        The value at the key, or default if navigation fails.
+        Empty list or dict.
+    
+    Examples:
+        >>> create_intermediate_container("0")
+        []
+        >>> create_intermediate_container(0)
+        []
+        >>> create_intermediate_container("name")
+        {}
+        >>> create_intermediate_container("-1")
+        []
     """
-    if isinstance(container, dict):
-        return container.get(key, default)
+    return [] if is_int_key(next_key) else {}
+
+
+MISSING = object()
+
+
+def navigate_dict_key(
+    current: dict,
+    key: Union[str, int],
+    *,
+    default: Any = MISSING,
+    raise_on_missing: bool = True
+) -> Any:
+    """Navigate into a dictionary using a key.
     
-    if isinstance(container, (list, tuple)):
-        if not is_int_key(key):
+    Args:
+        current: The dictionary to navigate into.
+        key: The key to access.
+        default: Value to return if key is missing (when not MISSING).
+        raise_on_missing: Whether to raise PathError on missing key.
+    
+    Returns:
+        The value at the key, or default if provided and key is missing.
+    
+    Raises:
+        PathError: If key is missing and raise_on_missing is True and default is MISSING.
+    """
+    if key not in current:
+        if default is not MISSING:
             return default
-        
-        idx = resolve_read_index(container, key)
-        if idx is None:
+        if raise_on_missing:
+            raise PathError(
+                f"Key '{key}' not found",
+                PathErrorCode.MISSING_KEY
+            )
+        return None
+    return current[key]
+
+
+def navigate_sequence_index(
+    current: Union[list, tuple],
+    key: Union[str, int],
+    *,
+    default: Any = MISSING,
+    raise_on_missing: bool = True
+) -> Any:
+    """Navigate into a list or tuple using an index.
+    
+    Args:
+        current: The list or tuple to navigate into.
+        key: The index to access.
+        default: Value to return if index is out of bounds (when not MISSING).
+        raise_on_missing: Whether to raise PathError on out-of-bounds index.
+    
+    Returns:
+        The value at the index, or default if provided and index is out of bounds.
+    
+    Raises:
+        PathError: If key is not a valid integer, or index is out of bounds and
+            raise_on_missing is True and default is MISSING.
+    """
+    if not is_int_key(key):
+        if default is not MISSING:
             return default
-        
-        return container[idx]
+        if raise_on_missing:
+            raise PathError(
+                f"Expected numeric index, got '{key}'",
+                PathErrorCode.INVALID_INDEX
+            )
+        return None
     
-    return default
+    idx = resolve_read_index(current, key)
+    if idx is None:
+        if default is not MISSING:
+            return default
+        if raise_on_missing:
+            raise PathError(
+                f"Index '{key}' out of bounds in path",
+                PathErrorCode.INVALID_INDEX
+            )
+        return None
+    
+    return current[idx]
 
 
-def create_container(strategy: FillStrategy, next_key: str) -> Union[dict, list]:
-    """Create a new container based on fill strategy and next key.
+def navigate_one_step(
+    current: Any,
+    key: Union[str, int],
+    *,
+    default: Any = MISSING,
+    raise_on_missing: bool = True
+) -> Any:
+    """Navigate one step into a nested structure.
+    
+    Handles dict, list, tuple, and other types.
     
     Args:
-        strategy: The fill strategy to use.
-        next_key: The next key in the path (used for "auto" strategy).
+        current: The current value in the nested structure.
+        key: The key or index to navigate with.
+        default: Value to return if navigation fails (when not MISSING).
+        raise_on_missing: Whether to raise PathError on navigation failure.
     
     Returns:
-        A new dict or list.
+        The next value in the navigation path, or default if provided and navigation fails.
+    
+    Raises:
+        PathError: If navigation fails and raise_on_missing is True and default is MISSING.
     """
-    if strategy == FillStrategy.DICT:
-        return {}
-    elif strategy == FillStrategy.LIST:
-        return []
-    else:  # auto or none
-        return [] if is_int_key(next_key) else {}
+    if isinstance(current, dict):
+        return navigate_dict_key(current, key, default=default, raise_on_missing=raise_on_missing)
+    
+    elif isinstance(current, (list, tuple)):
+        return navigate_sequence_index(current, key, default=default, raise_on_missing=raise_on_missing)
+    
+    else:
+        if default is not MISSING:
+            return default
+        if raise_on_missing:
+            raise PathError(
+                f"Cannot navigate into {type(current).__name__} at '{key}'",
+                PathErrorCode.NON_NAVIGABLE_TYPE
+            )
+        return None
 
 
-def fill_list_gaps(target: list, up_to_index: int, strategy: FillStrategy) -> None:
-    """Fill gaps in a list up to (but not including) target index.
+def navigate_to_parent(
+    data: Any,
+    intermediate_keys: List[Union[str, int]],
+    final_key: Union[str, int],
+    *,
+    create: bool = False
+) -> Any:
+    """Navigate to the parent container of the final key.
+    
+    For intermediate keys, creates containers if create=True. When create=True,
+    this function will also replace None values with appropriate containers (dict
+    or list) based on the next key type, allowing navigation through None values.
     
     Args:
-        target: The list to extend.
-        up_to_index: The target index to reach.
-        strategy: How to fill the gaps (None for auto/none, dict/list for others).
+        data: The root data structure.
+        intermediate_keys: List of intermediate keys to navigate through.
+        final_key: The final key (used to determine container type for last intermediate).
+        create: If True, automatically create missing intermediate containers and
+            replace None values with containers.
+    
+    Returns:
+        The parent container of the final key.
+    
+    Raises:
+        PathError: If path doesn't exist and create=False, or if attempting
+            to modify tuple, or other navigation errors.
     """
-    while len(target) < up_to_index:
-        if strategy == FillStrategy.DICT:
-            target.append({})
-        elif strategy == FillStrategy.LIST:
-            target.append([])
-        else:  # auto or none
-            target.append(None)
-
-
-def ensure_container_at_index(
-    target: list, 
-    index: int, 
-    strategy: FillStrategy, 
-    next_key: str
+    current = data
+    
+    # Navigate intermediate keys
+    for i, key in enumerate(intermediate_keys):
+        next_key = intermediate_keys[i + 1] if i + 1 < len(intermediate_keys) else final_key
+        
+        if isinstance(current, dict):
+            if key not in current:
+                if not create:
+                    raise PathError(
+                        f"Key '{key}' does not exist. Use create=True to auto-create path.",
+                        PathErrorCode.MISSING_KEY
+                    )
+                # Create intermediate container based on next key type
+                current[key] = create_intermediate_container(next_key)
+            elif current[key] is None:
+                if not create:
+                    raise PathError(
+                        f"Key '{key}' is None. Use create=True to replace with container.",
+                        PathErrorCode.MISSING_KEY
+                    )
+                current[key] = create_intermediate_container(next_key)
+            
+            current = current[key]
+        
+        elif isinstance(current, list):
+            if not is_int_key(key):
+                raise PathError(
+                    f"Expected numeric index for list, got '{key}'",
+                    PathErrorCode.INVALID_INDEX
+                )
+            
+            idx = resolve_write_index(current, key)
+            
+            # Extend list if needed (only for append, not gaps)
+            if idx == len(current):
+                if not create:
+                    raise PathError(
+                        f"Index {idx} does not exist. Use create=True to append.",
+                        PathErrorCode.INVALID_INDEX
+                    )
+                current.append(create_intermediate_container(next_key))
+            elif current[idx] is None:
+                if not create:
+                    raise PathError(
+                        f"Index {idx} is None. Use create=True to replace with container.",
+                        PathErrorCode.MISSING_KEY
+                    )
+                current[idx] = create_intermediate_container(next_key)
+            
+            current = current[idx]
+        
+        elif isinstance(current, tuple):
+            raise PathError(
+                "Cannot modify tuple (immutable container)",
+                PathErrorCode.IMMUTABLE_CONTAINER
+            )
+        
+        else:
+            raise PathError(
+                f"Cannot navigate into {type(current).__name__}",
+                PathErrorCode.NON_NAVIGABLE_TYPE
+            )
+    
+    return current
+
+
+def set_final_value(
+    parent: Union[dict, list],
+    key: Union[str, int],
+    value: Any,
+    *,
+    create: bool = False
 ) -> None:
-    """Ensure there's a navigable container at the given index.
+    """Set the final value at the given key in parent container.
     
-    Creates a new container if index doesn't exist or contains None.
+    Handles dict assignment and list append/modify logic.
     
     Args:
-        target: The list to modify.
-        index: The index to ensure a container at.
-        strategy: How to create containers.
-        next_key: The next key in the path (for "auto" strategy).
+        parent: The parent container (dict or list).
+        key: The key or index to set.
+        value: The value to set.
+        create: If True, allow appending to lists.
+    
+    Raises:
+        PathError: If setting fails (e.g., out of bounds, immutable container).
+    """
+    if isinstance(parent, dict):
+        parent[key] = value
+    
+    elif isinstance(parent, list):
+        if not is_int_key(key):
+            raise PathError(
+                f"Expected numeric index for list, got '{key}'",
+                PathErrorCode.INVALID_INDEX
+            )
+        
+        idx = resolve_write_index(parent, key)
+        
+        # Extend list if appending
+        if idx == len(parent):
+            if not create:
+                raise PathError(
+                    f"Index {idx} does not exist. Use create=True to append.",
+                    PathErrorCode.INVALID_INDEX
+                )
+            parent.append(value)
+        else:
+            parent[idx] = value
+    
+    elif isinstance(parent, tuple):
+        raise PathError(
+            "Cannot modify tuple (immutable container)",
+            PathErrorCode.IMMUTABLE_CONTAINER
+        )
+    
+    else:
+        raise PathError(
+            f"Cannot set value in {type(parent).__name__}",
+            PathErrorCode.NON_NAVIGABLE_TYPE
+        )
+
+
+def navigate_to_parent_for_delete(
+    data: Any,
+    keys: List[Union[str, int]]
+) -> Any:
+    """Navigate to the parent container of the final key for deletion.
+    
+    Raises PathError if any intermediate key is missing.
+    
+    Args:
+        data: The root data structure.
+        keys: List of keys to navigate through (excluding final key).
+    
+    Returns:
+        The parent container of the final key.
+    
+    Raises:
+        PathError: If any intermediate key is missing or navigation fails.
     """
-    if len(target) == index:
-        target.append(create_container(strategy, next_key))
-    elif target[index] is None:
-        target[index] = create_container(strategy, next_key)
\ No newline at end of file
+    current = data
+    
+    for key in keys:
+        if isinstance(current, dict):
+            if key not in current:
+                raise PathError(
+                    f"Key '{key}' not found",
+                    PathErrorCode.MISSING_KEY
+                )
+            current = current[key]
+        
+        elif isinstance(current, (list, tuple)):
+            if not is_int_key(key):
+                raise PathError(
+                    f"Expected numeric index, got '{key}'",
+                    PathErrorCode.INVALID_INDEX
+                )
+            
+            idx = resolve_read_index(current, key)
+            if idx is None:
+                raise PathError(
+                    f"Index '{key}' out of bounds",
+                    PathErrorCode.INVALID_INDEX
+                )
+            current = current[idx]
+        
+        else:
+            raise PathError(
+                f"Cannot navigate through {type(current).__name__}",
+                PathErrorCode.NON_NAVIGABLE_TYPE
+            )
+    
+    return current
+
+
+def delete_from_container(
+    parent: Union[dict, list],
+    key: Union[str, int],
+    *,
+    allow_list_mutation: bool = False
+) -> Any:
+    """Delete and return value from parent container.
+    
+    Handles dict.pop() and list.pop() with validation.
+    
+    Args:
+        parent: The parent container (dict or list).
+        key: The key or index to delete.
+        allow_list_mutation: If True, allows deletion from lists.
+    
+    Returns:
+        The deleted value.
+    
+    Raises:
+        PathError: If deletion fails (e.g., key not found, immutable container,
+            list mutation disabled).
+    """
+    if isinstance(parent, dict):
+        if key not in parent:
+            raise PathError(
+                f"Key '{key}' not found",
+                PathErrorCode.MISSING_KEY
+            )
+        return parent.pop(key)
+    
+    elif isinstance(parent, list):
+        if not allow_list_mutation:
+            raise PathError(
+                "List deletion disabled. Set allow_list_mutation=True",
+                PathErrorCode.OPERATION_DISABLED
+            )
+        
+        if not is_int_key(key):
+            raise PathError(
+                f"Expected numeric index, got '{key}'",
+                PathErrorCode.INVALID_INDEX
+            )
+        
+        idx = resolve_read_index(parent, key)
+        if idx is None:
+            raise PathError(
+                f"Index '{key}' out of bounds",
+                PathErrorCode.INVALID_INDEX
+            )
+        return parent.pop(idx)
+    
+    elif isinstance(parent, tuple):
+        raise PathError(
+            "Cannot delete from tuple (immutable)",
+            PathErrorCode.IMMUTABLE_CONTAINER
+        )
+    
+    else:
+        raise PathError(
+            f"Cannot delete from {type(parent).__name__}",
+            PathErrorCode.NON_NAVIGABLE_TYPE
+        )
\ No newline at end of file
diff --git a/nestedutils/introspection.py b/nestedutils/introspection.py
new file mode 100644
index 0000000..5aa3fc9
--- /dev/null
+++ b/nestedutils/introspection.py
@@ -0,0 +1,126 @@
+"""Introspection utilities for nested data structures.
+
+This module provides functions to inspect and analyze nested data structures
+without modifying them. All functions are pure and support dict, list, and tuple.
+Other container types (set, frozenset, deque, etc.) are treated as leaf values.
+"""
+from typing import Any, List, Union
+
+
+def get_depth(data: Any) -> int:
+    """Return the maximum nesting depth of a nested structure.
+
+    Supports dict, list, and tuple. Other types are treated as leaves (depth 0).
+
+    Args:
+        data: Any nested structure (dict, list, tuple, or primitive).
+
+    Returns:
+        Integer depth. Primitives return 0, empty containers return 1.
+
+    Examples:
+        >>> get_depth(42)
+        0
+        >>> get_depth({})
+        1
+        >>> get_depth({"a": 1})
+        1
+        >>> get_depth({"a": {"b": 1}})
+        2
+        >>> get_depth({"a": {"b": {"c": 1}}})
+        3
+        >>> get_depth([1, [2, [3]]])
+        3
+    """
+    if isinstance(data, dict):
+        if not data:
+            return 1
+        return 1 + max(get_depth(v) for v in data.values())
+
+    elif isinstance(data, (list, tuple)):
+        if not data:
+            return 1
+        return 1 + max(get_depth(item) for item in data)
+
+    return 0
+
+
+def count_leaves(data: Any) -> int:
+    """Count the total number of leaf values in a nested structure.
+
+    A leaf is any value that is not a dict, list, or tuple.
+    Empty containers count as 0 leaves.
+
+    Supports dict, list, and tuple. Other container types (set, frozenset, etc.)
+    are treated as single leaf values.
+
+    Args:
+        data: Any nested structure.
+
+    Returns:
+        Integer count of leaf values.
+
+    Examples:
+        >>> count_leaves(42)
+        1
+        >>> count_leaves({})
+        0
+        >>> count_leaves({"a": 1, "b": 2})
+        2
+        >>> count_leaves({"a": {"b": 1, "c": 2}, "d": 3})
+        3
+        >>> count_leaves([1, 2, [3, 4]])
+        4
+    """
+    if isinstance(data, dict):
+        return sum(count_leaves(v) for v in data.values())
+
+    elif isinstance(data, (list, tuple)):
+        return sum(count_leaves(item) for item in data)
+
+    return 1
+
+
+def get_all_paths(data: Any) -> List[List[Union[str, int]]]:
+    """Return all paths to leaf values in a nested structure.
+
+    Supports dict, list, and tuple. Other container types are treated as leaves.
+
+    Args:
+        data: Any nested structure.
+
+    Returns:
+        List of paths, where each path is a list of keys/indices.
+
+    Examples:
+        >>> get_all_paths({"a": 1, "b": 2})
+        [["a"], ["b"]]
+        >>> get_all_paths({"a": {"b": 1, "c": 2}})
+        [["a", "b"], ["a", "c"]]
+        >>> get_all_paths({"users": [{"name": "Alice"}, {"name": "Bob"}]})
+        [["users", 0, "name"], ["users", 1, "name"]]
+        >>> get_all_paths({})
+        []
+        >>> get_all_paths(42)
+        [[]]
+    """
+    def recurse(current: Any, prefix: List[Union[str, int]]) -> List[List[Union[str, int]]]:
+        if isinstance(current, dict):
+            if not current:
+                return []
+            paths = []
+            for key, value in current.items():
+                paths.extend(recurse(value, prefix + [key]))
+            return paths
+
+        elif isinstance(current, (list, tuple)):
+            if not current:
+                return []
+            paths = []
+            for idx, item in enumerate(current):
+                paths.extend(recurse(item, prefix + [idx]))
+            return paths
+
+        return [prefix]
+
+    return recurse(data, [])
diff --git a/pyproject.toml b/pyproject.toml
index f76c9ff..48ca05d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "nestedutils"
-version = "1.1.7"
+version = "2.0.0"
 description = "The lightweight Python library for safe, simple, dot-notation access to nested dicts and lists. Effortlessly get, set, and delete values deep in your complex JSON, API responses, and config files without verbose error-checking or handling KeyError exceptions."
 readme = "README.md"
 requires-python = ">=3.8"
diff --git a/tests/test_delete.py b/tests/test_delete.py
index 3c63c18..0554390 100644
--- a/tests/test_delete.py
+++ b/tests/test_delete.py
@@ -38,12 +38,12 @@ def test_delete_from_nested_list_dict(self):
 class TestDeleteListOperations:
     """Tests for deleting from lists."""
     
-    def test_delete_list_index_disallowed(self):
+    def test_delete_list_requires_allow_list_mutation_flag(self):
         """Delete list index without allow_list_mutation should fail."""
         d = {"a": [1, 2, 3]}
         with pytest.raises(PathError) as exc_info:
             delete_at(d, "a.1")
-        assert exc_info.value.code == PathErrorCode.INVALID_PATH
+        assert exc_info.value.code == PathErrorCode.OPERATION_DISABLED
     
     def test_delete_list_index_allowed(self):
         """Delete list index with allow_list_mutation=True."""
@@ -148,14 +148,14 @@ def test_delete_path_invalid_type(self):
         d = {"a": 5}
         with pytest.raises(PathError) as exc_info:
             delete_at(d, "a.b")
-        assert exc_info.value.code == PathErrorCode.INVALID_PATH
-    
+        assert exc_info.value.code == PathErrorCode.NON_NAVIGABLE_TYPE
+
     def test_delete_from_none(self):
         """Delete from None should fail."""
         d = {"a": None}
         with pytest.raises(PathError) as exc_info:
             delete_at(d, "a.b")
-        assert exc_info.value.code == PathErrorCode.INVALID_PATH
+        assert exc_info.value.code == PathErrorCode.NON_NAVIGABLE_TYPE
     
     def test_delete_from_tuple(self):
         """Delete from tuple should fail (immutable)."""
@@ -206,14 +206,14 @@ def test_delete_after_set(self):
         """Delete value that was just set."""
         d = {}
         from nestedutils import set_at
-        set_at(d, "a.b.c", 1)
+        set_at(d, "a.b.c", 1, create=True)
         val = delete_at(d, "a.b.c")
         assert val == 1
         assert d == {"a": {"b": {}}}
 
 
-class TestDeleteInvalidPaths:
-    """Tests for invalid path types in delete_at."""
+class TestDeletePathFormats:
+    """Tests for different path formats in delete_at."""
     
     def test_delete_path_as_list(self):
         """Delete using list form path."""
diff --git a/tests/test_edge_cases.py b/tests/test_edge_cases.py
index d64af72..34b6850 100644
--- a/tests/test_edge_cases.py
+++ b/tests/test_edge_cases.py
@@ -1,5 +1,5 @@
 import pytest
-from nestedutils import get_at, set_at, delete_at, exists_at
+from nestedutils import get_at, set_at, delete_at
 from nestedutils.exceptions import PathError, PathErrorCode
 
 
@@ -38,9 +38,10 @@ def test_all_error_codes_exist(self):
             PathErrorCode.EMPTY_PATH,
             PathErrorCode.IMMUTABLE_CONTAINER,
             PathErrorCode.INVALID_PATH,
-            PathErrorCode.INVALID_FILL_STRATEGY,
+            PathErrorCode.NON_NAVIGABLE_TYPE,
+            PathErrorCode.OPERATION_DISABLED,
         ]
-        assert len(codes) == 6
+        assert len(codes) == 7
     
     def test_error_code_values(self):
         """Verify error code string values."""
@@ -49,18 +50,8 @@ def test_error_code_values(self):
         assert PathErrorCode.EMPTY_PATH.value == "EMPTY_PATH"
         assert PathErrorCode.IMMUTABLE_CONTAINER.value == "IMMUTABLE_CONTAINER"
         assert PathErrorCode.INVALID_PATH.value == "INVALID_PATH"
-        assert PathErrorCode.INVALID_FILL_STRATEGY.value == "INVALID_FILL_STRATEGY"
-
-
-class TestPathNormalizationEdgeCases:
-    """Additional edge cases for path normalization."""
-    
-    def test_path_list_with_negative_index(self):
-        """List form path with negative index."""
-        d = {"a": [10, 20, 30]}
-        assert get_at(d, ["a", -1]) == 30
-        set_at(d, ["a", -1], 999)
-        assert d["a"][2] == 999
+        assert PathErrorCode.NON_NAVIGABLE_TYPE.value == "NON_NAVIGABLE_TYPE"
+        assert PathErrorCode.OPERATION_DISABLED.value == "OPERATION_DISABLED"
 
 
 class TestComplexIntegrationScenarios:
@@ -69,39 +60,29 @@ class TestComplexIntegrationScenarios:
     def test_round_trip_operations(self):
         """Multiple operations in sequence."""
         d = {}
-        set_at(d, "a.b.c", 1)
+        set_at(d, "a.b.c", 1, create=True)
         assert get_at(d, "a.b.c") == 1
-        set_at(d, "a.b.d", 2)
+        set_at(d, "a.b.d", 2, create=True)
         assert get_at(d, "a.b.d") == 2
         val = delete_at(d, "a.b.c")
         assert val == 1
-        assert get_at(d, "a.b.c") is None
+        with pytest.raises(PathError):
+            get_at(d, "a.b.c")
         assert get_at(d, "a.b.d") == 2
     
     def test_mixed_numeric_and_string_keys(self):
         """Mixed numeric and string keys."""
         d = {}
-        set_at(d, "a.0.b.1.c", 42)
+        # Build structure sequentially - first create index 0, then index 1
+        set_at(d, "a.0.b.0.c", 10, create=True)  # Create list at a[0]["b"] with first element
+        set_at(d, "a.0.b.1.c", 42, create=True)  # Now can append to list
         assert isinstance(d["a"], list)
         assert isinstance(d["a"][0], dict)
         assert isinstance(d["a"][0]["b"], list)
+        assert d["a"][0]["b"][0]["c"] == 10
         assert d["a"][0]["b"][1]["c"] == 42
 
 
-class TestEmptyAndNoneValues:
-    """Tests for empty and None value handling."""
-    
-    def test_get_none_vs_missing(self):
-        """Distinguish between None value and missing key."""
-        d1 = {"a": None}
-        d2 = {}
-        assert get_at(d1, "a") is None
-        assert get_at(d2, "a") is None
-        # Both return None, but one has the key, one doesn't
-        assert "a" in d1
-        assert "a" not in d2
-
-
 class TestLargeStructures:
     """Tests for large data structures."""
     
@@ -109,19 +90,19 @@ def test_very_deep_nesting(self):
         """Very deeply nested structure."""
         d = {}
         path = ".".join(["level" + str(i) for i in range(20)])
-        set_at(d, path, "deep")
+        set_at(d, path, "deep", create=True)
         assert get_at(d, path) == "deep"
     
     def test_many_keys_in_dict(self):
         """Dict with many keys."""
         d = {}
         for i in range(100):
-            set_at(d, f"key{i}", i)
+            set_at(d, f"key{i}", i, create=True)
         for i in range(100):
             assert get_at(d, f"key{i}") == i
 
 
-class TestTypeCoercion:
+class TestListPathTypeHandling:
     """Tests for type coercion and conversion."""
     
     def test_list_path_with_string_numbers(self):
@@ -129,13 +110,7 @@ def test_list_path_with_string_numbers(self):
         d = {"a": [1, 2, 3]}
         assert get_at(d, ["a", "0"]) == 1
         assert get_at(d, ["a", "1"]) == 2
-    
-    def test_list_path_with_integers(self):
-        """List form path with actual integers."""
-        d = {"a": [1, 2, 3]}
-        assert get_at(d, ["a", 0]) == 1
-        assert get_at(d, ["a", 1]) == 2
-    
+
     def test_mixed_path_types(self):
         """Mixed path types in list form."""
         d = {"a": {"0": [1, 2, 3]}}
@@ -148,82 +123,35 @@ class TestSpecialCharacters:
     def test_keys_with_special_chars(self):
         """Keys with special characters."""
         d = {}
-        set_at(d, "a-b.c_d.e@f", 42)
+        set_at(d, "a-b.c_d.e@f", 42, create=True)
         assert get_at(d, "a-b.c_d.e@f") == 42
     
     def test_keys_with_spaces_in_list_form(self):
         """Keys with spaces using list form."""
         d = {}
-        set_at(d, ["key with spaces", "another key"], 1)
+        set_at(d, ["key with spaces", "another key"], 1, create=True)
         assert get_at(d, ["key with spaces", "another key"]) == 1
     
     def test_keys_with_newlines_in_list_form(self):
         """Keys with newlines using list form."""
         d = {}
-        set_at(d, ["key\nwith\nnewlines"], 1)
+        set_at(d, ["key\nwith\nnewlines"], 1, create=True)
         assert get_at(d, ["key\nwith\nnewlines"]) == 1
 
 
 class TestNegativeIndexEdgeCases:
-    """Comprehensive edge cases for negative indices."""
-    
-    def test_negative_index_boundary_conditions(self):
-        """Test negative indices at boundaries."""
-        d = {"a": [10, 20, 30]}
-        # Valid negative indices
-        assert get_at(d, "a.-1") == 30
-        assert get_at(d, "a.-2") == 20
-        assert get_at(d, "a.-3") == 10
-        # Just out of bounds
-        assert get_at(d, "a.-4") is None
-        assert get_at(d, "a.-5") is None
-    
-    def test_negative_index_single_element_list(self):
-        """Negative index on single element list."""
-        d = {"a": [42]}
-        assert get_at(d, "a.-1") == 42
-        assert get_at(d, "a.-2") is None
-        # Can modify with negative index
-        set_at(d, "a.-1", 99)
-        assert d["a"] == [99]
-    
-    def test_negative_index_in_intermediate_path(self):
-        """Negative index used in intermediate path steps."""
-        d = {"data": [[1, 2], [3, 4], [5, 6]]}
-        # Navigate using negative index, then access nested
-        assert get_at(d, "data.-1.0") == 5
-        assert get_at(d, "data.-2.-1") == 4
-        # Set using negative index in intermediate path
-        set_at(d, "data.-1.-1", 99)
-        assert d["data"][-1] == [5, 99]
-    
-    def test_negative_index_with_tuples(self):
-        """Negative index works with tuples (read-only)."""
-        d = {"a": (10, 20, 30)}
-        assert get_at(d, "a.-1") == 30
-        assert get_at(d, "a.-2") == 20
-        assert exists_at(d, "a.-1") is True
-        assert exists_at(d, "a.-4") is False
-        # Cannot modify tuples
-        with pytest.raises(PathError) as exc_info:
-            set_at(d, "a.-1", 99)
-        assert exc_info.value.code == PathErrorCode.IMMUTABLE_CONTAINER
-    
+    """Edge cases for negative indices not covered in operation-specific tests."""
+
     def test_negative_index_very_large_negative(self):
         """Very large negative numbers should be out of bounds."""
         d = {"a": [1, 2, 3]}
-        assert get_at(d, "a.-1000") is None
-        assert get_at(d, "a.-999999") is None
-        # Should not raise, just return default
-    
-    def test_negative_index_chaining(self):
-        """Chaining multiple negative index operations."""
-        d = {"levels": [[[1, 2], [3, 4]], [[5, 6], [7, 8]]]}
-        # Navigate through multiple levels using negative indices
-        assert get_at(d, "levels.-1.-1.-1") == 8
-        assert get_at(d, "levels.-1.-1.-2") == 7
-        assert get_at(d, "levels.-2.-1.-1") == 4
-    
+        with pytest.raises(PathError):
+            get_at(d, "a.-1000")
+        with pytest.raises(PathError):
+            get_at(d, "a.-999999")
+        # With default, returns default
+        assert get_at(d, "a.-1000", default="missing") == "missing"
+
     def test_negative_index_after_list_mutation(self):
         """Negative index behavior after list mutations."""
         d = {"items": [1, 2, 3, 4, 5]}
@@ -235,5 +163,64 @@ def test_negative_index_after_list_mutation(self):
         assert get_at(d, "items.-2") == 4
         assert get_at(d, "items.-4") == 1
         # -5 should now be out of bounds
-        assert get_at(d, "items.-5") is None
+        with pytest.raises(PathError):
+            get_at(d, "items.-5")
+
+
+class TestMissingEdgeCases:
+    """Additional edge cases for comprehensive coverage."""
+
+    def test_get_empty_path_raises(self):
+        """Empty path should raise EMPTY_PATH error."""
+        with pytest.raises(PathError) as exc:
+            get_at({}, "")
+        assert exc.value.code == PathErrorCode.EMPTY_PATH
+
+    def test_set_empty_path_raises(self):
+        """Empty path should raise EMPTY_PATH error for set_at."""
+        with pytest.raises(PathError) as exc:
+            set_at({}, "", 1)
+        assert exc.value.code == PathErrorCode.EMPTY_PATH
+
+    def test_delete_empty_path_raises(self):
+        """Empty path should raise EMPTY_PATH error for delete_at."""
+        with pytest.raises(PathError) as exc:
+            delete_at({}, "")
+        assert exc.value.code == PathErrorCode.EMPTY_PATH
+
+    def test_set_non_container_root_raises(self):
+        """Setting on non-container root should raise NON_NAVIGABLE_TYPE."""
+        with pytest.raises(PathError) as exc:
+            set_at(42, "a", 1)
+        assert exc.value.code == PathErrorCode.NON_NAVIGABLE_TYPE
+
+    def test_get_non_container_root_raises(self):
+        """Getting from non-container root should raise NON_NAVIGABLE_TYPE."""
+        with pytest.raises(PathError) as exc:
+            get_at(42, "a")
+        assert exc.value.code == PathErrorCode.NON_NAVIGABLE_TYPE
+
+    def test_delete_non_container_root_raises(self):
+        """Deleting from non-container root should raise NON_NAVIGABLE_TYPE."""
+        with pytest.raises(PathError) as exc:
+            delete_at(42, "a")
+        assert exc.value.code == PathErrorCode.NON_NAVIGABLE_TYPE
+
+    def test_get_from_set_raises(self):
+        """Accessing set elements should raise NON_NAVIGABLE_TYPE."""
+        with pytest.raises(PathError) as exc:
+            get_at({"a": {1, 2, 3}}, "a.0")
+        assert exc.value.code == PathErrorCode.NON_NAVIGABLE_TYPE
+
+    def test_get_from_frozenset_raises(self):
+        """Accessing frozenset elements should raise NON_NAVIGABLE_TYPE."""
+        with pytest.raises(PathError) as exc:
+            get_at({"a": frozenset([1, 2, 3])}, "a.0")
+        assert exc.value.code == PathErrorCode.NON_NAVIGABLE_TYPE
+
+    def test_set_into_string_raises(self):
+        """Setting into a string should raise NON_NAVIGABLE_TYPE."""
+        with pytest.raises(PathError) as exc:
+            set_at({"a": "hello"}, "a.0", "x")
+        assert exc.value.code == PathErrorCode.NON_NAVIGABLE_TYPE
 
diff --git a/tests/test_exists.py b/tests/test_exists.py
index 3c0e6eb..9dc50da 100644
--- a/tests/test_exists.py
+++ b/tests/test_exists.py
@@ -107,14 +107,6 @@ def test_exists_path_list_with_negative_index_nested(self):
         assert exists_at(d, ["items", -2, "name"]) is True
         assert exists_at(d, ["items", -5, "name"]) is False
     
-    def test_exists_unicode_keys(self):
-        """Check existence with unicode keys."""
-        d = {}
-        d["你好"] = {"world": {"🌍": 42}}
-        assert exists_at(d, "你好.world.🌍") is True
-        assert exists_at(d, "你好.world.🌎") is False
-        assert exists_at(d, ["你好", "world", "🌍"]) is True
-    
     def test_exists_keys_with_dots_in_list_form(self):
         """List form allows keys with dots."""
         d = {"a.b": {"c.d": 10}}
@@ -157,12 +149,6 @@ def test_exists_empty_string_value(self):
         d = {"a": ""}
         assert exists_at(d, "a") is True
     
-    def test_exists_very_deep_nesting(self):
-        """Check existence in very deeply nested structure."""
-        d = {"a": {"b": {"c": {"d": {"e": {"f": {"g": 42}}}}}}}
-        assert exists_at(d, "a.b.c.d.e.f.g") is True
-        assert exists_at(d, "a.b.c.d.e.f.h") is False
-    
     def test_exists_from_dict_with_numeric_keys(self):
         """Check existence in dict with numeric string keys."""
         d = {"0": {"1": {"2": 5}}}
@@ -221,7 +207,7 @@ def test_exists_after_set(self):
         from nestedutils import set_at
         d = {}
         assert exists_at(d, "a.b.c") is False
-        set_at(d, "a.b.c", 1)
+        set_at(d, "a.b.c", 1, create=True)
         assert exists_at(d, "a.b.c") is True
     
     def test_exists_after_delete(self):
@@ -233,15 +219,17 @@ def test_exists_after_delete(self):
         assert exists_at(d, "a.b") is False
         assert exists_at(d, "a.c") is True
     
-    def test_exists_with_sparse_list(self):
-        """Check existence in sparse list created with fill_strategy."""
+    def test_exists_with_sequential_list(self):
+        """Check existence in sequentially built list."""
         from nestedutils import set_at
         d = {}
-        set_at(d, "items.5", "Item 6", fill_strategy="none")
-        assert exists_at(d, "items.5") is True
-        assert exists_at(d, "items.0") is True  # None values exist
-        assert exists_at(d, "items.4") is True  # None values exist
-        assert exists_at(d, "items.6") is False
+        set_at(d, "items.0", "Item 1", create=True)
+        set_at(d, "items.1", "Item 2", create=True)
+        set_at(d, "items.2", "Item 3", create=True)
+        assert exists_at(d, "items.0") is True
+        assert exists_at(d, "items.1") is True
+        assert exists_at(d, "items.2") is True
+        assert exists_at(d, "items.3") is False
     
     def test_exists_root_level(self):
         """Check existence at root level."""
@@ -256,7 +244,7 @@ def test_exists_nested_none_replacement(self):
         d = {"a": None}
         assert exists_at(d, "a") is True
         assert exists_at(d, "a.b") is False
-        set_at(d, "a.b.c", 10)
+        set_at(d, "a.b.c", 10, create=True)
         assert exists_at(d, "a") is True
         assert exists_at(d, "a.b") is True
         assert exists_at(d, "a.b.c") is True
diff --git a/tests/test_get.py b/tests/test_get.py
index 5e3c7ac..2bdcb6b 100644
--- a/tests/test_get.py
+++ b/tests/test_get.py
@@ -35,11 +35,17 @@ def test_get_intermediate_nested_object(self):
         # Can also get deeper values
         assert get_at(data, "user.profile.address.city") == "SF"
     
-    def test_get_missing_returns_default(self):
-        """Get missing key returns default value."""
+    def test_get_missing_raises_error(self):
+        """Get missing key raises PathError by default."""
+        d = {"a": {"b": 1}}
+        with pytest.raises(PathError) as exc_info:
+            get_at(d, "a.c")
+        assert exc_info.value.code == PathErrorCode.MISSING_KEY
+    
+    def test_get_missing_with_default(self):
+        """Get missing key returns default when explicitly provided."""
         d = {"a": {"b": 1}}
         assert get_at(d, "a.c", default=99) == 99
-        assert get_at(d, "x.y.z") is None
         assert get_at(d, "x.y.z", default="missing") == "missing"
     
     def test_get_list_index(self):
@@ -64,11 +70,12 @@ def test_get_negative_index_nested_structure(self):
         assert get_at(d, "items.-1") == {"name": "banana"}
     
     def test_get_negative_index_out_of_bounds(self):
-        """Get with out-of-bounds negative index returns default."""
+        """Get with out-of-bounds negative index raises PathError by default."""
         d = {"items": [{"name": "apple"}, {"name": "banana"}]}
-        assert get_at(d, "items.-5.name") is None
+        with pytest.raises(PathError) as exc_info:
+            get_at(d, "items.-5.name")
+        assert exc_info.value.code == PathErrorCode.INVALID_INDEX
         assert get_at(d, "items.-5.name", default="not found") == "not found"
-        assert get_at(d, "items.-10") is None
     
     def test_get_negative_index_deeply_nested(self):
         """Get with negative index in deeply nested structure."""
@@ -84,20 +91,28 @@ def test_get_nested_list_dict_mix(self):
         assert get_at(d, "a.0.b") == 1
     
     def test_get_list_index_out_of_bounds(self):
-        """Get from out-of-bounds list index returns default."""
+        """Get from out-of-bounds list index raises PathError by default."""
         d = {"a": [10, 20]}
-        assert get_at(d, "a.5") is None
+        with pytest.raises(PathError) as exc_info:
+            get_at(d, "a.5")
+        assert exc_info.value.code == PathErrorCode.INVALID_INDEX
         assert get_at(d, "a.5", default=-1) == -1
-        assert get_at(d, "a.-10") is None
+        with pytest.raises(PathError):
+            get_at(d, "a.-10")
         # Test both positive and negative out-of-bounds
-        assert get_at(d, "a.100") is None
-        assert get_at(d, "a.-100") is None
-        assert get_at(d, "a.-3") is None  # Just out of bounds for length 2
+        with pytest.raises(PathError):
+            get_at(d, "a.100")
+        with pytest.raises(PathError):
+            get_at(d, "a.-100")
+        with pytest.raises(PathError):
+            get_at(d, "a.-3")  # Just out of bounds for length 2
     
     def test_get_list_index_non_integer(self):
-        """Get with non-integer key on list returns default."""
+        """Get with non-integer key on list raises PathError by default."""
         d = {"a": [1]}
-        assert get_at(d, "a.x") is None
+        with pytest.raises(PathError) as exc_info:
+            get_at(d, "a.x")
+        assert exc_info.value.code == PathErrorCode.INVALID_INDEX
         assert get_at(d, "a.x", default="not found") == "not found"
 
 
@@ -139,24 +154,26 @@ def test_keys_with_dots_in_list_form(self):
         d = {"a.b": {"c.d": 10}}
         assert get_at(d, ["a.b", "c.d"]) == 10
     
-    def test_complex_keys_in_list_form(self):
-        """List form handles any key type: special characters, dots, integers."""
+    def test_integer_vs_string_key_distinction(self):
+        """List form handles any key type: special characters, dots, integers (preserved or converted)."""
         # Create data structure with complex keys
         data = {
             "user-info": {
                 "first.name": {
-                    123: "found it!"
+                    "123": "string_key_value",  # String key
+                    123: "int_key_value"  # Integer key
                 }
             }
         }
         
         # Verify each level works independently
-        assert get_at(data, ["user-info"]) == {"first.name": {123: "found it!"}}
-        assert get_at(data, ["user-info", "first.name"]) == {123: "found it!"}
+        assert get_at(data, ["user-info"]) == {"first.name": {"123": "string_key_value", 123: "int_key_value"}}
+        assert get_at(data, ["user-info", "first.name"]) == {"123": "string_key_value", 123: "int_key_value"}
         
-        # String form cannot handle these keys (dots would be interpreted as separators)
-        # But list form works perfectly
-        assert get_at(data, ["user-info", "first.name", 123]) == "found it!"
+        # Integer in path accesses integer key (preserved)
+        assert get_at(data, ["user-info", "first.name", 123]) == "int_key_value"
+        # String in path accesses string key
+        assert get_at(data, ["user-info", "first.name", "123"]) == "string_key_value"
         
         # Test with default for missing path
         assert get_at(data, ["user-info", "first.name", 999], default="not found") == "not found"
@@ -166,15 +183,22 @@ class TestGetEdgeCases:
     """Edge cases for get_at."""
     
     def test_get_empty_dict(self):
-        """Get from empty dict."""
+        """Get from empty dict raises PathError by default."""
         d = {}
-        assert get_at(d, "a") is None
-        assert get_at(d, "a.b.c") is None
+        with pytest.raises(PathError):
+            get_at(d, "a")
+        with pytest.raises(PathError):
+            get_at(d, "a.b.c")
+        # With default, returns default
+        assert get_at(d, "a", default=None) is None
+        assert get_at(d, "a.b.c", default="missing") == "missing"
     
     def test_get_empty_list(self):
-        """Get from empty list."""
+        """Get from empty list raises PathError by default."""
         d = {"a": []}
-        assert get_at(d, "a.0") is None
+        with pytest.raises(PathError):
+            get_at(d, "a.0")
+        assert get_at(d, "a.0", default=None) is None
     
     def test_get_none_value(self):
         """Get None value explicitly stored."""
@@ -182,28 +206,34 @@ def test_get_none_value(self):
         assert get_at(d, "a") is None
     
     def test_none_blocks_navigation(self):
-        """None as intermediate value should block navigation and return default."""
+        """None as intermediate value should block navigation and raise PathError by default."""
         # None at first level blocks further navigation
         d = {"a": None}
-        assert get_at(d, "a.b") is None
+        with pytest.raises(PathError):
+            get_at(d, "a.b")
         assert get_at(d, "a.b", default="missing") == "missing"
-        assert get_at(d, "a.b.c") is None
+        with pytest.raises(PathError):
+            get_at(d, "a.b.c")
         assert get_at(d, "a.b.c", default=99) == 99
         
         # None at deeper level also blocks navigation
         d2 = {"a": {"b": None}}
-        assert get_at(d2, "a.b.c") is None
+        with pytest.raises(PathError):
+            get_at(d2, "a.b.c")
         assert get_at(d2, "a.b.c", default="not found") == "not found"
-        assert get_at(d2, "a.b.c.d.e") is None
+        with pytest.raises(PathError):
+            get_at(d2, "a.b.c.d.e")
         
         # None in list should also block navigation
         d3 = {"items": [None, {"name": "apple"}]}
-        assert get_at(d3, "items.0.name") is None
+        with pytest.raises(PathError):
+            get_at(d3, "items.0.name")
         assert get_at(d3, "items.0.name", default="no name") == "no name"
         
         # None in nested structure
         d4 = {"data": {"user": None, "other": {"value": 42}}}
-        assert get_at(d4, "data.user.name") is None
+        with pytest.raises(PathError):
+            get_at(d4, "data.user.name")
         assert get_at(d4, "data.user.name", default="default") == "default"
         # But other paths should still work
         assert get_at(d4, "data.other.value") == 42
@@ -224,37 +254,31 @@ def test_get_empty_string_value(self):
         d = {"a": ""}
         assert get_at(d, "a") == ""
     
-    def test_get_very_deep_nesting(self):
-        """Get from very deeply nested structure."""
-        d = {"a": {"b": {"c": {"d": {"e": {"f": {"g": 42}}}}}}}
-        assert get_at(d, "a.b.c.d.e.f.g") == 42
-    
     def test_get_from_dict_with_numeric_keys(self):
         """Get from dict with numeric string keys."""
         d = {"0": {"1": {"2": 5}}}
         assert get_at(d, "0.1.2") == 5
     
     def test_get_dict_with_integer_vs_string_keys(self):
-        """Test that integer and string keys are correctly distinguished.
+        """Test that integer keys in paths are preserved and can access integer dict keys.
         
-        The library correctly preserves key types in list form paths, allowing
-        access to both integer keys and string keys with the same numeric value.
+        normalize_path() now preserves integer types from list paths, allowing
+        dictionaries with integer keys to be accessed using integer values in paths.
         """
         # Dictionary with both integer key and string key
         data = {0: "int_value", "0": "string_value"}
         
-        # Using integer in path accesses integer key
-        assert get_at(data, [0]) == "int_value"
-        
-        # Using string in path accesses string key
-        assert get_at(data, ["0"]) == "string_value"
+        # Integer in path accesses integer key
+        assert get_at(data, [0]) == "int_value"  # Preserves int, accesses int key
+        # String in path accesses string key
+        assert get_at(data, ["0"]) == "string_value"  # String accesses string key
         
-        # Verify direct access matches
+        # Verify direct access still distinguishes
         assert data[0] == "int_value"
         assert data["0"] == "string_value"
         
-        # Both keys are distinct and accessible
-        assert get_at(data, [0]) != get_at(data, ["0"])
+        # List paths now distinguish between integer and string keys
+        assert get_at(data, [0]) != get_at(data, ["0"])  # Different keys, different values
     
     def test_get_mixed_types(self):
         """Get from structure with mixed types."""
diff --git a/tests/test_introspection.py b/tests/test_introspection.py
new file mode 100644
index 0000000..5608a5a
--- /dev/null
+++ b/tests/test_introspection.py
@@ -0,0 +1,229 @@
+import pytest
+from nestedutils import get_depth, count_leaves, get_all_paths
+
+
+class TestGetDepth:
+    """Tests for get_depth function."""
+
+    def test_primitive_values(self):
+        """Primitives have depth 0."""
+        assert get_depth(42) == 0
+        assert get_depth("string") == 0
+        assert get_depth(3.14) == 0
+        assert get_depth(True) == 0
+        assert get_depth(None) == 0
+
+    def test_empty_containers(self):
+        """Empty containers have depth 1."""
+        assert get_depth({}) == 1
+        assert get_depth([]) == 1
+        assert get_depth(()) == 1
+
+    def test_flat_dict(self):
+        """Flat dict with primitives has depth 1."""
+        assert get_depth({"a": 1}) == 1
+        assert get_depth({"a": 1, "b": 2, "c": 3}) == 1
+
+    def test_flat_list(self):
+        """Flat list with primitives has depth 1."""
+        assert get_depth([1, 2, 3]) == 1
+        assert get_depth([1]) == 1
+
+    def test_nested_dict(self):
+        """Nested dicts increase depth."""
+        assert get_depth({"a": {"b": 1}}) == 2
+        assert get_depth({"a": {"b": {"c": 1}}}) == 3
+        assert get_depth({"a": {"b": {"c": {"d": 1}}}}) == 4
+
+    def test_nested_list(self):
+        """Nested lists increase depth."""
+        assert get_depth([[1]]) == 2
+        assert get_depth([[[1]]]) == 3
+        assert get_depth([1, [2, [3]]]) == 3
+
+    def test_mixed_nesting(self):
+        """Mixed dict and list nesting."""
+        assert get_depth({"a": [1, 2]}) == 2
+        assert get_depth([{"a": 1}]) == 2
+        assert get_depth({"a": [{"b": 1}]}) == 3
+        assert get_depth({"users": [{"profile": {"name": "Alice"}}]}) == 4
+
+    def test_uneven_depth(self):
+        """Returns maximum depth when branches have different depths."""
+        data = {
+            "shallow": 1,
+            "deep": {"nested": {"value": 1}}
+        }
+        assert get_depth(data) == 3
+
+    def test_tuple_support(self):
+        """Tuples are treated like lists."""
+        assert get_depth((1, 2, 3)) == 1
+        assert get_depth({"a": (1, 2)}) == 2
+        assert get_depth(({"a": 1}, {"b": 2})) == 2
+
+    def test_set_treated_as_leaf(self):
+        """Sets are treated as leaf values (depth 0)."""
+        assert get_depth({1, 2, 3}) == 0
+        assert get_depth({"a": {1, 2, 3}}) == 1
+
+
+class TestCountLeaves:
+    """Tests for count_leaves function."""
+
+    def test_primitive_values(self):
+        """Primitives count as 1 leaf."""
+        assert count_leaves(42) == 1
+        assert count_leaves("string") == 1
+        assert count_leaves(3.14) == 1
+        assert count_leaves(True) == 1
+        assert count_leaves(None) == 1
+
+    def test_empty_containers(self):
+        """Empty containers have 0 leaves."""
+        assert count_leaves({}) == 0
+        assert count_leaves([]) == 0
+        assert count_leaves(()) == 0
+
+    def test_flat_dict(self):
+        """Flat dict counts each value as a leaf."""
+        assert count_leaves({"a": 1}) == 1
+        assert count_leaves({"a": 1, "b": 2}) == 2
+        assert count_leaves({"a": 1, "b": 2, "c": 3}) == 3
+
+    def test_flat_list(self):
+        """Flat list counts each element as a leaf."""
+        assert count_leaves([1]) == 1
+        assert count_leaves([1, 2, 3]) == 3
+        assert count_leaves([1, 2, 3, 4, 5]) == 5
+
+    def test_nested_dict(self):
+        """Nested dicts still count only leaf values."""
+        assert count_leaves({"a": {"b": 1}}) == 1
+        assert count_leaves({"a": {"b": 1, "c": 2}}) == 2
+        assert count_leaves({"a": {"b": 1}, "d": 2}) == 2
+
+    def test_nested_list(self):
+        """Nested lists still count only leaf values."""
+        assert count_leaves([[1]]) == 1
+        assert count_leaves([[1, 2], [3]]) == 3
+        assert count_leaves([1, [2, [3, 4]]]) == 4
+
+    def test_mixed_nesting(self):
+        """Mixed dict and list nesting."""
+        data = {
+            "a": {"b": 1, "c": 2},
+            "d": [3, 4, 5],
+            "e": 6
+        }
+        assert count_leaves(data) == 6
+
+    def test_complex_structure(self):
+        """Complex nested structure."""
+        data = {
+            "users": [
+                {"name": "Alice", "age": 30},
+                {"name": "Bob", "age": 25}
+            ],
+            "meta": {"count": 2}
+        }
+        assert count_leaves(data) == 5  # Alice, 30, Bob, 25, 2
+
+    def test_tuple_support(self):
+        """Tuples are counted like lists."""
+        assert count_leaves((1, 2, 3)) == 3
+        assert count_leaves({"a": (1, 2)}) == 2
+
+    def test_set_treated_as_leaf(self):
+        """Sets are treated as single leaf values."""
+        assert count_leaves({1, 2, 3}) == 1
+        assert count_leaves({"a": {1, 2, 3}}) == 1
+
+
+class TestGetAllPaths:
+    """Tests for get_all_paths function."""
+
+    def test_primitive_value(self):
+        """Primitive returns empty path."""
+        assert get_all_paths(42) == [[]]
+        assert get_all_paths("string") == [[]]
+        assert get_all_paths(None) == [[]]
+
+    def test_empty_containers(self):
+        """Empty containers return no paths."""
+        assert get_all_paths({}) == []
+        assert get_all_paths([]) == []
+        assert get_all_paths(()) == []
+
+    def test_flat_dict(self):
+        """Flat dict returns single-key paths."""
+        result = get_all_paths({"a": 1, "b": 2})
+        assert ["a"] in result
+        assert ["b"] in result
+        assert len(result) == 2
+
+    def test_flat_list(self):
+        """Flat list returns index paths."""
+        assert get_all_paths([1, 2, 3]) == [[0], [1], [2]]
+
+    def test_nested_dict(self):
+        """Nested dicts produce nested paths."""
+        result = get_all_paths({"a": {"b": 1, "c": 2}})
+        assert ["a", "b"] in result
+        assert ["a", "c"] in result
+        assert len(result) == 2
+
+    def test_nested_list(self):
+        """Nested lists produce nested index paths."""
+        assert get_all_paths([[1, 2], [3]]) == [[0, 0], [0, 1], [1, 0]]
+
+    def test_mixed_dict_list(self):
+        """Mixed dict and list nesting."""
+        data = {"users": [{"name": "Alice"}, {"name": "Bob"}]}
+        result = get_all_paths(data)
+        assert ["users", 0, "name"] in result
+        assert ["users", 1, "name"] in result
+        assert len(result) == 2
+
+    def test_complex_structure(self):
+        """Complex nested structure."""
+        data = {
+            "a": {
+                "b": 1,
+                "c": [2, 3]
+            },
+            "d": 4
+        }
+        result = get_all_paths(data)
+        assert ["a", "b"] in result
+        assert ["a", "c", 0] in result
+        assert ["a", "c", 1] in result
+        assert ["d"] in result
+        assert len(result) == 4
+
+    def test_tuple_support(self):
+        """Tuples are handled like lists."""
+        data = {"items": (1, 2)}
+        result = get_all_paths(data)
+        assert ["items", 0] in result
+        assert ["items", 1] in result
+
+    def test_set_treated_as_leaf(self):
+        """Sets are treated as leaf values."""
+        data = {"a": {1, 2, 3}}
+        result = get_all_paths(data)
+        assert result == [["a"]]
+
+    def test_deeply_nested(self):
+        """Deeply nested structure."""
+        data = {"a": {"b": {"c": {"d": {"e": 1}}}}}
+        assert get_all_paths(data) == [["a", "b", "c", "d", "e"]]
+
+    def test_path_types(self):
+        """Paths contain strings for dict keys and ints for list indices."""
+        data = {"key": [1, 2]}
+        result = get_all_paths(data)
+        assert result == [["key", 0], ["key", 1]]
+        # Verify types
+        assert isinstance(result[0][0], str)
+        assert isinstance(result[0][1], int)
diff --git a/tests/test_normalize_path.py b/tests/test_normalize_path.py
index fb2002c..222a744 100644
--- a/tests/test_normalize_path.py
+++ b/tests/test_normalize_path.py
@@ -23,7 +23,7 @@ class TestNormalizePathValid:
         (["a", "b"], ["a", "b"]),
         (["a", "b", "c"], ["a", "b", "c"]),
         
-        # List paths - mixed types (converted to strings)
+        # List paths - integers preserved
         (["user", 0, "name"], ["user", 0, "name"]),
         ([0, 1, 2], [0, 1, 2]),
         (["items", -1], ["items", -1]),
diff --git a/tests/test_set.py b/tests/test_set.py
index bb84364..be2762b 100644
--- a/tests/test_set.py
+++ b/tests/test_set.py
@@ -19,22 +19,30 @@ def test_set_nested_existing(self):
         assert d == {"a": {"b": {"c": 9}}}
     
     def test_set_auto_create_dicts(self):
-        """Auto-create nested dicts when setting."""
+        """Auto-create nested dicts when setting with create=True."""
         d = {}
-        set_at(d, "x.y.z", 10)
+        set_at(d, "x.y.z", 10, create=True)
         assert d == {"x": {"y": {"z": 10}}}
     
     def test_set_auto_create_lists(self):
-        """Auto-create lists when using numeric keys."""
+        """Auto-create lists when using numeric keys with create=True."""
         d = {}
-        set_at(d, "a.0.b", 1)
+        set_at(d, "a.0.b", 1, create=True)
         assert d == {"a": [{"b": 1}]}
     
-    def test_set_auto_sparse_list(self):
-        """Auto-create sparse list with None fill."""
+    def test_set_requires_create_for_missing_path(self):
+        """set_at raises PathError for missing paths by default."""
+        d = {}
+        with pytest.raises(PathError) as exc_info:
+            set_at(d, "x.y.z", 10)
+        assert exc_info.value.code == PathErrorCode.MISSING_KEY
+    
+    def test_set_no_sparse_lists(self):
+        """Sparse list creation is not allowed."""
         d = {"a": []}
-        set_at(d, "a.5", 99)
-        assert d == {"a": [None, None, None, None, None, 99]}
+        with pytest.raises(PathError) as exc_info:
+            set_at(d, "a.5", 99, create=True)
+        assert exc_info.value.code == PathErrorCode.INVALID_INDEX
     
     def test_set_negative_index_write(self):
         """Set value using negative index."""
@@ -71,7 +79,7 @@ def test_set_negative_index_intermediate_path(self):
         assert d["data"][-1][-1] == 99
         assert d["data"][-1] == [5, 99]
     
-    def test_set_negative_index_extends_list(self):
+    def test_set_negative_index_modifies_single_element_list(self):
         """Negative index on short list should still work."""
         d = {"a": [1]}
         set_at(d, "a.-1", 99)
@@ -89,99 +97,64 @@ def test_set_negative_index_all_valid_indices(self):
     def test_set_inside_list_of_dicts(self):
         """Set value inside list containing dicts."""
         d = {"a": [{}]}
-        set_at(d, "a.0.x.y", 5)
+        set_at(d, "a.0.x.y", 5, create=True)
         assert d == {"a": [{"x": {"y": 5}}]}
 
 
-class TestSetFillStrategy:
-    """Tests for fill_strategy parameter."""
-    
-    def test_set_fill_strategy_none(self):
-        """Fill strategy 'none' fills missing list items with None."""
-        d = {}
-        set_at(d, "a.3", 7, fill_strategy="none")
-        assert d == {"a": [None, None, None, 7]}
+class TestSetCreateFlag:
+    """Tests for create parameter."""
     
-    def test_set_fill_strategy_dict(self):
-        """Fill strategy 'dict' always creates dicts."""
+    def test_set_create_true_auto_creates(self):
+        """create=True auto-creates missing intermediate containers."""
         d = {}
-        set_at(d, "a.0.b", 1, fill_strategy="dict")
-        assert d == {"a": {"0": {"b": 1}}}
-    
-    def test_set_fill_strategy_list(self):
-        """Fill strategy 'list' always creates lists."""
-        d = {}
-        set_at(d, "a.0.1", 42, fill_strategy="list")
-        assert d == {"a": [[None, 42]]}
+        set_at(d, "a.b.c", 1, create=True)
+        assert d == {"a": {"b": {"c": 1}}}
     
-    def test_set_invalid_fill_strategy(self):
-        """Invalid fill_strategy should raise PathError."""
+    def test_set_create_false_raises_for_missing(self):
+        """create=False (default) raises PathError for missing paths."""
         d = {}
         with pytest.raises(PathError) as exc_info:
-            set_at(d, "a.b", 1, fill_strategy="unknown")
-        assert exc_info.value.code == PathErrorCode.INVALID_FILL_STRATEGY
+            set_at(d, "a.b.c", 1)
+        assert exc_info.value.code == PathErrorCode.MISSING_KEY
     
-    def test_all_numeric_path_with_dict_strategy(self):
-        """Numeric strings should be dict keys with dict strategy."""
+    def test_set_create_true_sequential_list_building(self):
+        """create=True allows sequential list building."""
         d = {}
-        set_at(d, "0.1.2", 5, fill_strategy="dict")
-        assert d == {"0": {"1": {"2": 5}}}
+        set_at(d, "items.0", "first", create=True)
+        set_at(d, "items.1", "second", create=True)
+        assert d == {"items": ["first", "second"]}
     
-    def test_all_numeric_path_with_auto_strategy(self):
-        """All numeric path with auto should create nested lists."""
-        d = {}
-        set_at(d, "0.1", 5, fill_strategy="auto")
-        assert isinstance(d["0"], list)
-        assert d["0"][1] == 5
-    
-    def test_multiple_operations_different_strategies(self):
-        """Multiple sets with different strategies on same structure."""
-        d = {}
-        set_at(d, "a.0", 1, fill_strategy="auto")
-        set_at(d, "a.5", 2, fill_strategy="dict")  # Should still be list
-        assert isinstance(d["a"], list)
-        assert len(d["a"]) == 6
-    
-    @pytest.mark.parametrize("strategy", ["auto", "none", "dict", "list"])
-    def test_fill_strategy_creates_correct_type(self, strategy):
-        """Each fill strategy creates appropriate container type."""
+    def test_set_create_true_no_gaps_allowed(self):
+        """create=True does not allow sparse lists."""
         d = {}
-        if strategy == "dict":
-            set_at(d, "a.b.c", 1, fill_strategy=strategy)
-            assert isinstance(d["a"], dict)
-            assert isinstance(d["a"]["b"], dict)
-        elif strategy == "list":
-            set_at(d, "a.0.1", 1, fill_strategy=strategy)
-            assert isinstance(d["a"], list)
-            assert isinstance(d["a"][0], list)
-        else:  # auto or none
-            set_at(d, "a.0.b", 1, fill_strategy=strategy)
-            assert isinstance(d["a"], list)
-            assert isinstance(d["a"][0], dict)
+        set_at(d, "items.0", "first", create=True)
+        with pytest.raises(PathError) as exc_info:
+            set_at(d, "items.5", "x", create=True)
+        assert exc_info.value.code == PathErrorCode.INVALID_INDEX
 
 
 class TestSetNoneValues:
     """Tests for handling None values."""
     
     def test_set_through_existing_none_in_list(self):
-        """Should replace None with a container when navigating deeper."""
+        """Should replace None with a container when navigating deeper with create=True."""
         d = {"a": [None, None, None]}
-        set_at(d, "a.1.x", 5)
+        set_at(d, "a.1.x", 5, create=True)
         assert d == {"a": [None, {"x": 5}, None]}
     
-    def test_set_through_none_created_by_sparse_fill(self):
-        """Auto-filled None should be replaceable."""
-        d = {}
-        set_at(d, "a.5", 1)  # Creates [None, None, None, None, None, 1]
-        set_at(d, "a.2.b", 99)  # Should replace None at index 2
-        assert d["a"][2] == {"b": 99}
-    
     def test_set_through_none_in_dict(self):
-        """Should replace None value in dict when navigating deeper."""
+        """Should replace None value in dict when navigating deeper with create=True."""
         d = {"a": None}
-        set_at(d, "a.b.c", 10)
+        set_at(d, "a.b.c", 10, create=True)
         assert d == {"a": {"b": {"c": 10}}}
     
+    def test_set_through_none_requires_create(self):
+        """Setting through None requires create=True."""
+        d = {"a": None}
+        with pytest.raises(PathError) as exc_info:
+            set_at(d, "a.b.c", 10)
+        assert exc_info.value.code == PathErrorCode.MISSING_KEY
+    
     def test_set_none_value_explicitly(self):
         """Setting None as a value should work."""
         d = {"a": 1}
@@ -189,16 +162,16 @@ def test_set_none_value_explicitly(self):
         assert d == {"a": None}
     
     def test_set_none_in_nested_path(self):
-        """Setting None deep in path."""
+        """Setting None deep in path with create=True."""
         d = {}
-        set_at(d, "a.b.c", None)
+        set_at(d, "a.b.c", None, create=True)
         assert d == {"a": {"b": {"c": None}}}
     
     def test_set_none_then_replace(self):
-        """Set None then replace with container."""
+        """Set None then replace with container using create=True."""
         d = {}
         set_at(d, "a", None)
-        set_at(d, "a.b", 1)
+        set_at(d, "a.b", 1, create=True)
         assert d == {"a": {"b": 1}}
 
 
@@ -242,7 +215,7 @@ def test_set_at_invalid_type(self):
         d = {"a": 1}
         with pytest.raises(PathError) as exc_info:
             set_at(d, "a.b", 10)
-        assert exc_info.value.code == PathErrorCode.INVALID_PATH
+        assert exc_info.value.code == PathErrorCode.NON_NAVIGABLE_TYPE
     
     def test_set_negative_index_on_empty_list(self):
         """Can't use negative index on empty list."""
@@ -254,11 +227,13 @@ def test_set_negative_index_on_empty_list(self):
     def test_set_negative_index_on_empty_dict(self):
         """Can't create list with negative index as first operation."""
         d = {}
+        # First, need to create the list with create=True
+        # But negative index can't be used to create (must reference existing element)
         with pytest.raises(PathError) as exc_info:
-            set_at(d, "a.-1", 5)
+            set_at(d, "a.-1", 5, create=True)
         assert exc_info.value.code == PathErrorCode.INVALID_INDEX
     
-    def test_numeric_key_on_existing_dict(self):
+    def test_set_numeric_string_creates_dict_key_not_list(self):
         """Setting numeric key on existing dict creates string key."""
         d = {"a": {"b": 1}}
         set_at(d, "a.0", 5)
@@ -267,19 +242,19 @@ def test_numeric_key_on_existing_dict(self):
     def test_invalid_negative_format(self):
         """String starting with - but not a valid negative number."""
         d = {}
-        set_at(d, "a.-5x", 1)
+        set_at(d, "a.-5x", 1, create=True)
         assert d == {"a": {"-5x": 1}}  # Should be dict key
     
     def test_just_minus_sign(self):
         """Just a minus sign should be dict key."""
         d = {}
-        set_at(d, "a.-", 1)
+        set_at(d, "a.-", 1, create=True)
         assert d == {"a": {"-": 1}}
     
     def test_multiple_minus_signs(self):
         """Multiple minus signs."""
         d = {}
-        set_at(d, "a.--5", 1)
+        set_at(d, "a.--5", 1, create=True)
         assert d == {"a": {"--5": 1}}
 
 
@@ -289,25 +264,19 @@ class TestSetPathNormalization:
     def test_path_as_list_form(self):
         """Set using list form path."""
         d = {}
-        set_at(d, ["a", "b", "c"], 1)
+        set_at(d, ["a", "b", "c"], 1, create=True)
         assert d == {"a": {"b": {"c": 1}}}
     
     def test_keys_with_dots_in_list_form(self):
         """Using list form allows keys with dots."""
         d = {}
-        set_at(d, ["a.b", "c.d"], 10)
+        set_at(d, ["a.b", "c.d"], 10, create=True)
         assert d == {"a.b": {"c.d": 10}}
     
-    def test_unicode_keys(self):
-        """Unicode in keys should work."""
-        d = {}
-        set_at(d, "你好.world.🌍", 42)
-        assert d["你好"]["world"]["🌍"] == 42
-    
     def test_path_list_with_integers(self):
         """List form path with integer keys."""
         d = {}
-        set_at(d, ["a", 0, "b"], 1)
+        set_at(d, ["a", 0, "b"], 1, create=True)
         assert d == {"a": [{"b": 1}]}
 
 
@@ -317,12 +286,14 @@ class TestSetComplex:
     def test_set_deep_mixed_structure(self):
         """Set in deeply nested mixed structure."""
         d = {}
-        set_at(d, "x.0.y.1.z", 42)
+        # Need to build sequentially - first create index 0, then index 1
+        set_at(d, "x.0.y.0.z", 10, create=True)  # Create first element
+        set_at(d, "x.0.y.1.z", 42, create=True)  # Now can append
         assert d == {
             "x": [
                 {
                     "y": [
-                        None,
+                        {"z": 10},
                         {"z": 42}
                     ]
                 }
@@ -330,9 +301,9 @@ def test_set_deep_mixed_structure(self):
         }
     
     def test_set_at_creates_correct_types_auto(self):
-        """Auto strategy creates correct types."""
+        """create=True creates correct types."""
         d = {}
-        set_at(d, "root.0.child.0", 10)
+        set_at(d, "root.0.child.0", 10, create=True)
         assert d == {"root": [{"child": [10]}]}
     
     def test_overwrite_value_with_container(self):
@@ -343,32 +314,27 @@ def test_overwrite_value_with_container(self):
         set_at(d, "a.c", 2)
         assert d == {"a": {"b": 1, "c": 2}}
     
-    def test_final_key_extends_list(self):
-        """Final key extending list should always fill with None."""
+    def test_final_key_extends_list_sequentially(self):
+        """Final key can only extend list by 1 (append)."""
         d = {"a": []}
-        set_at(d, "a.5", 99)
-        assert d == {"a": [None, None, None, None, None, 99]}
+        set_at(d, "a.0", "first", create=True)
+        set_at(d, "a.1", "second", create=True)
+        assert d == {"a": ["first", "second"]}
     
-    def test_set_positive_extension_from_docstring(self):
-        """Positive index extension example from docstring."""
+    def test_set_positive_extension_sequential_only(self):
+        """Positive index can only append, not create gaps."""
         data = [1, 2, 3]
-        set_at(data, "5", 99)
-        assert data == [1, 2, 3, None, None, 99]
-    
-    def test_very_large_sparse_list(self):
-        """Creating very large sparse list should work."""
-        d = {}
-        set_at(d, "a.1000", 1)
-        assert len(d["a"]) == 1001
-        assert d["a"][1000] == 1
-        assert all(d["a"][i] is None for i in range(1000))
+        set_at(data, "3", 99, create=True)  # Append
+        assert data == [1, 2, 3, 99]
+        with pytest.raises(PathError):
+            set_at(data, "5", 100, create=True)  # Would create gap
     
     def test_set_multiple_values_same_structure(self):
         """Set multiple values in same structure."""
         d = {}
-        set_at(d, "a.b.c", 1)
-        set_at(d, "a.b.d", 2)
-        set_at(d, "a.e", 3)
+        set_at(d, "a.b.c", 1, create=True)
+        set_at(d, "a.b.d", 2, create=True)  # Path exists now, no create needed
+        set_at(d, "a.e", 3, create=True)  # Path exists now, no create needed
         assert d == {"a": {"b": {"c": 1, "d": 2}, "e": 3}}
     
     def test_set_overwrite_existing_value(self):
diff --git a/uv.lock b/uv.lock
index c141aa8..e081e31 100644
--- a/uv.lock
+++ b/uv.lock
@@ -837,7 +837,7 @@ wheels = [
 
 [[package]]
 name = "nestedutils"
-version = "1.1.7"
+version = "2.0.0"
 source = { editable = "." }
 
 [package.dev-dependencies]