diff --git a/create_trace_mapping.py b/create_trace_mapping.py
index 2b8ef57..1dc449a 100644
--- a/create_trace_mapping.py
+++ b/create_trace_mapping.py
@@ -1,3 +1,5 @@
+from pathlib import Path
+
 import yaml
 from generator_to_trace_draft_mapper import (
     draft_solar_generator_to_trace_mapping,
@@ -19,14 +21,14 @@
 solar_generator_mapping = draft_solar_generator_to_trace_mapping(
     solar_gens, solar_traces
 )
-with open("draft_solar_generator_mapping.yaml", "w") as file:
+with Path("draft_solar_generator_mapping.yaml").open("w") as file:
     yaml.dump(solar_generator_mapping, file, default_flow_style=False)
 
 
 solar_traces = "/media/nick/Samsung_T5/isp_2024_data/trace_data/solar/solar_2023"
 rezs = gets_rezs(workbook)
 solar_rez_mapping = draft_solar_rez_mapping(rezs, solar_traces)
-with open("solar_area_mapping.yaml", "w") as file:
+with Path("solar_area_mapping.yaml").open("w") as file:
     yaml.dump(solar_rez_mapping, file, default_flow_style=False)
 
 duids_and_station_names = static_table(
@@ -47,12 +49,12 @@
 wind_generator_mapping = draft_wind_generator_to_trace_mapping(
     wind_gens, wind_duids_and_station_names, wind_traces
 )
-with open("draft_wind_generator_mapping.yaml", "w") as file:
+with Path("draft_wind_generator_mapping.yaml").open("w") as file:
     yaml.dump(wind_generator_mapping, file, default_flow_style=False, sort_keys=False)
 
 
 wind_traces = "D:/isp_2024_data/trace_data/wind/wind_2023"
 rezs = gets_rezs(workbook)
 wind_rez_mapping = draft_wind_rez_mapping(rezs, wind_traces)
-with open("draft_wind_rez_mapping.yaml", "w") as file:
+with Path("draft_wind_rez_mapping.yaml").open("w") as file:
     yaml.dump(wind_rez_mapping, file, default_flow_style=False)
diff --git a/src/isp_trace_parser/__init__.py b/src/isp_trace_parser/__init__.py
index 648baeb..0101b45 100644
--- a/src/isp_trace_parser/__init__.py
+++ b/src/isp_trace_parser/__init__.py
@@ -15,13 +15,13 @@
 from isp_trace_parser.wind_traces import WindMetadataFilter, parse_wind_traces
 
 __all__ = [
-    "trace_formatter",
+    "DemandMetadataFilter",
+    "SolarMetadataFilter",
+    "WindMetadataFilter",
+    "construct_reference_year_mapping",
     "get_data",
-    "parse_wind_traces",
     "parse_demand_traces",
     "parse_solar_traces",
-    "construct_reference_year_mapping",
-    "WindMetadataFilter",
-    "SolarMetadataFilter",
-    "DemandMetadataFilter",
+    "parse_wind_traces",
+    "trace_formatter",
 ]
diff --git a/src/isp_trace_parser/construct_reference_year_mapping.py b/src/isp_trace_parser/construct_reference_year_mapping.py
index 95b9299..b79ba76 100644
--- a/src/isp_trace_parser/construct_reference_year_mapping.py
+++ b/src/isp_trace_parser/construct_reference_year_mapping.py
@@ -13,7 +13,7 @@
 @validate_call
 def construct_reference_year_mapping(
     start_year: int, end_year: int, reference_years: list[int]
-):
+) -> dict:
     """Constructs a dictionary mapping a sequence of modeling years to a cycle of reference years.
 
     Examples:
@@ -42,4 +42,4 @@ def construct_reference_year_mapping(
         reference_years = (
             reference_years * full_reference_year_cycles
         ) + reference_years[:partial_cycle_length]
-    return dict(zip(years, reference_years))
+    return dict(zip(years, reference_years, strict=True))
diff --git a/src/isp_trace_parser/demand_trace_metadata.py b/src/isp_trace_parser/demand_trace_metadata.py
index 7a1eff9..2b77896 100644
--- a/src/isp_trace_parser/demand_trace_metadata.py
+++ b/src/isp_trace_parser/demand_trace_metadata.py
@@ -29,7 +29,8 @@ def build(
         refyear, _, dimensions_suffix = after.partition("_")
         key = (location_prefix, dimensions_suffix)
         if not refyear.isdigit() or key not in lookup:
-            raise ValueError(f"Unexpected trace filename: {path.name}")
+            msg = f"Unexpected trace filename: {path.name}"
+            raise ValueError(msg)
         file_metadata[path] = {**lookup[key], "reference_year": int(refyear)}
     return file_metadata
 
diff --git a/src/isp_trace_parser/demand_traces.py b/src/isp_trace_parser/demand_traces.py
index 56b71d8..4a0a690 100644
--- a/src/isp_trace_parser/demand_traces.py
+++ b/src/isp_trace_parser/demand_traces.py
@@ -8,7 +8,7 @@
 import functools
 import os
 from pathlib import Path
-from typing import Literal, Optional
+from typing import Literal
 
 import polars as pl
 from joblib import Parallel, delayed
@@ -52,15 +52,16 @@ class DemandMetadataFilter(BaseModel):
         reference_year: list of ints specifying reference_years
     """
 
-    subregion: Optional[list[str]] = None
-    scenario: Optional[
+    subregion: list[str] | None = None
+    scenario: (
         list[Literal["Step Change", "Progressive Change", "Green Energy Exports"]]
-    ] = None
-    poe: Optional[list[Literal["POE50", "POE10"]]] = None
-    demand_type: Optional[
-        list[Literal["OPSO_MODELLING", "OPSO_MODELLING_PVLITE", "PV_TOT"]]
-    ] = None
-    reference_year: Optional[list[int]] = None
+        | None
+    ) = None
+    poe: list[Literal["POE50", "POE10"]] | None = None
+    demand_type: (
+        list[Literal["OPSO_MODELLING", "OPSO_MODELLING_PVLITE", "PV_TOT"]] | None
+    ) = None
+    reference_year: list[int] | None = None
 
 
 @validate_call
@@ -69,7 +70,7 @@ def parse_demand_traces(
     parsed_directory: str | Path,
     use_concurrency: bool = True,
     filters: DemandMetadataFilter | None = None,
-):
+) -> None:
     """Takes a directory with AEMO demand trace data and reformats the data, saving it to a new directory.
 
     AEMO demand trace data comes in CSVs with columns specifying the year, day, and month, and data columns
diff --git a/src/isp_trace_parser/get_data.py b/src/isp_trace_parser/get_data.py
index e058aa4..1cf4f91 100644
--- a/src/isp_trace_parser/get_data.py
+++ b/src/isp_trace_parser/get_data.py
@@ -7,7 +7,7 @@
 
 import datetime
 from pathlib import Path
-from typing import List, Literal
+from typing import Literal
 
 import pandas as pd
 import polars as pl
@@ -16,7 +16,7 @@
 
 def _year_range_to_dt_range(
     start_year: int, end_year: int, year_type: Literal["fy", "calendar"] = "fy"
-):
+) -> datetime.datetime:
     """
     Convert year range to datetime boundaries for efficient time filtering.
 
@@ -44,10 +44,11 @@ def _year_range_to_dt_range(
             end_year, 7, 1
         )
 
-    elif year_type == "calendar":
+    if year_type == "calendar":
         return datetime.datetime(start_year, 1, 1), datetime.datetime(
             end_year + 1, 1, 1
         )
+    raise ValueError(year_type)
 
 
 def _query_parquet_single_reference_year(
@@ -55,8 +56,8 @@ def _query_parquet_single_reference_year(
     end_year: int,
     reference_year: int,
     directory: str | Path,
-    filters: dict[str, any] = None,
-    select_columns: list[str] = None,
+    filters: dict[str, any] | None = None,
+    select_columns: list[str] | None = None,
     year_type: Literal["fy", "calendar"] = "fy",
 ) -> pd.DataFrame:
     """
@@ -143,8 +144,7 @@ def _query_parquet_multiple_reference_years(
                 start_year=year, end_year=year, reference_year=reference_year, **kwargs
             )
         )
-    data = pd.concat(data).reset_index(drop=True)
-    return data
+    return pd.concat(data).reset_index(drop=True)
 
 
 @validate_call
@@ -152,11 +152,11 @@ def get_project_single_reference_year(
     start_year: int,
     end_year: int,
     reference_year: int,
-    project: str | List,
+    project: str | list,
     directory: str | Path,
     year_type: Literal["fy", "calendar"] = "fy",
-    select_columns: list[str] = None,
-):
+    select_columns: list[str] | None = None,
+) -> pd.DataFrame:
     """
     Query project trace data for a single reference year.
 
@@ -244,12 +244,12 @@ def get_zone_single_reference_year(
     start_year: int,
     end_year: int,
     reference_year: int,
-    zone: str | List,
-    resource_type: str | List,
+    zone: str | list,
+    resource_type: str | list,
     directory: str | Path,
     year_type: Literal["fy", "calendar"] = "fy",
-    select_columns: list[str] = None,
-):
+    select_columns: list[str] | None = None,
+) -> pd.DataFrame:
     """
     Query zone trace data for a single reference year.
 
@@ -340,14 +340,14 @@ def get_demand_single_reference_year(
     start_year: int,
     end_year: int,
     reference_year: int,
-    scenario: str | List,
-    subregion: str | List,
-    demand_type: str | List,
-    poe: str | List,
+    scenario: str | list,
+    subregion: str | list,
+    demand_type: str | list,
+    poe: str | list,
     directory: str | Path,
     year_type: Literal["fy", "calendar"] = "fy",
-    select_columns: list[str] = None,
-):
+    select_columns: list[str] | None = None,
+) -> pd.DataFrame:
     """
     Query demand trace data for a single reference year.
 
@@ -448,11 +448,11 @@ def get_demand_single_reference_year(
 @validate_call
 def get_project_multiple_reference_years(
     reference_year_mapping: dict[int, int],
-    project: str | List,
+    project: str | list,
     directory: str | Path,
     year_type: Literal["fy", "calendar"] = "fy",
-    select_columns: list[str] = None,
-):
+    select_columns: list[str] | None = None,
+) -> pd.DataFrame:
     """
     Query project trace data across multiple reference years.
 
@@ -537,12 +537,12 @@ def get_project_multiple_reference_years(
 @validate_call
 def get_zone_multiple_reference_years(
     reference_year_mapping: dict[int, int],
-    zone: str | List,
-    resource_type: str | List,
+    zone: str | list,
+    resource_type: str | list,
     directory: str | Path,
     year_type: Literal["fy", "calendar"] = "fy",
-    select_columns: list[str] = None,
-):
+    select_columns: list[str] | None = None,
+) -> pd.DataFrame:
     """
     Query zone trace data across multiple reference years.
 
@@ -630,14 +630,14 @@ def get_zone_multiple_reference_years(
 @validate_call
 def get_demand_multiple_reference_years(
     reference_year_mapping: dict[int, int],
-    scenario: str | List,
-    subregion: str | List,
-    demand_type: str | List,
-    poe: str | List,
+    scenario: str | list,
+    subregion: str | list,
+    demand_type: str | list,
+    poe: str | list,
     directory: str | Path,
     year_type: Literal["fy", "calendar"] = "fy",
-    select_columns: list[str] = None,
-):
+    select_columns: list[str] | None = None,
+) -> pd.DataFrame:
     """
     Query demand trace data across multiple reference years.
 
diff --git a/src/isp_trace_parser/input_validation.py b/src/isp_trace_parser/input_validation.py
index 6c696a3..a56cc44 100644
--- a/src/isp_trace_parser/input_validation.py
+++ b/src/isp_trace_parser/input_validation.py
@@ -11,7 +11,7 @@
 def input_directory(path: Path | str) -> Path:
     path = is_valid_path(path)
     if not path.is_dir():
-        raise ValueError(f"Directory {path} does not exist")
+        raise FileNotFoundError(path)
     return path
 
 
@@ -22,10 +22,12 @@ def parsed_directory(path: str | Path) -> Path:
 def is_valid_path(path: str | Path) -> Path:
     try:
         return Path(path)
-    except (TypeError, ValueError):
-        raise ValueError(f"Invalid parsed directory path: {path}")
+    except (TypeError, ValueError) as exc:
+        msg = f"Invalid parsed directory path: {path}"
+        raise ValueError(msg) from exc
 
 
-def start_year_before_end_year(start_year, end_year):
+def start_year_before_end_year(start_year: int, end_year: int) -> None:
     if end_year < start_year:
-        raise ValueError(f"Start year {end_year} < end year {start_year}")
+        msg = f"Start year {end_year} < end year {start_year}"
+        raise ValueError(msg)
diff --git a/src/isp_trace_parser/optimise_parquet.py b/src/isp_trace_parser/optimise_parquet.py
index 9ced190..a549377 100644
--- a/src/isp_trace_parser/optimise_parquet.py
+++ b/src/isp_trace_parser/optimise_parquet.py
@@ -7,7 +7,6 @@
 
 from itertools import product
 from pathlib import Path
-from typing import Optional
 
 import duckdb
 from pydantic import validate_call
@@ -30,7 +29,7 @@ def partition_traces_by_columns(
     input_directory: str | Path,
     output_directory: str | Path,
     partition_cols: list[str],
-    sort_by: Optional[list[str]] = ["datetime"],
+    sort_by: list[str] | None = None,
 ) -> None:
     """Partition parquet traces by specified columns with optional sorting.
 
@@ -60,6 +59,12 @@ def partition_traces_by_columns(
         ...     partition_cols=["scenario", "reference_year"]
         ... ) # doctest: +SKIP
     """
+
+    if sort_by is None:
+        # Avoid use of mutable data structure for argument defaults
+        # (see Ruff rule B006).
+        sort_by = ["datetime"]
+
     output_path = Path(output_directory)
     output_path.mkdir(parents=True, exist_ok=True)
 
@@ -71,23 +76,21 @@ def partition_traces_by_columns(
         values = con.execute(f"""
             SELECT DISTINCT {col}
             FROM read_parquet('{input_directory}')
-        """).fetchall()
+        """).fetchall()  # noqa: S608
         distinct_values.append(values)
 
     partitions = [tuple(val[0] for val in vals) for vals in product(*distinct_values)]
 
     for partition_values in partitions:
-        # print(*partition_values)
-
         conditions = []
-        for col, val in zip(partition_cols, partition_values):
+        for col, val in zip(partition_cols, partition_values, strict=True):
             if isinstance(val, str):
                 conditions.append(f"{col}='{val}'")
             else:
                 conditions.append(f"{col}={val}")
 
         where_clause = " AND ".join(conditions)
-        query = f"SELECT * FROM read_parquet('{input_directory}') WHERE {where_clause}"
+        query = f"SELECT * FROM read_parquet('{input_directory}') WHERE {where_clause}"  # noqa: S608
 
         if sort_by:
             query += f" ORDER BY {', '.join(sort_by)}"
diff --git a/src/isp_trace_parser/remote/download.py b/src/isp_trace_parser/remote/download.py
index 17c751f..d16bfbd 100644
--- a/src/isp_trace_parser/remote/download.py
+++ b/src/isp_trace_parser/remote/download.py
@@ -61,14 +61,15 @@ def _download_from_manifest(
     manifest_path = files("isp_trace_parser.remote.manifests") / f"{manifest_name}.txt"
 
     if not manifest_path.exists():
-        raise FileNotFoundError(f"Manifest file not found: {manifest_path}")
+        raise FileNotFoundError(manifest_path)
 
     # Read URLs from manifest
-    with open(manifest_path) as f:
+    with Path(manifest_path).open("r") as f:
         urls = [line.strip() for line in f if line.strip()]
 
     if not urls:
-        raise ValueError(f"No URLs found in manifest: {manifest_path}")
+        msg = f"No URLs found in manifest: {manifest_path}"
+        raise ValueError(msg)
 
     save_directory = Path(save_directory)
 
@@ -88,12 +89,13 @@ def _download_with_retry(
     for attempt in range(max_retries):
         try:
             _download_file(url, save_directory, strip_levels, unquote_path)
-            return
-        except requests.exceptions.RequestException:
+        except requests.exceptions.RequestException:  # noqa: PERF203
             if attempt < max_retries - 1:
                 time.sleep(2**attempt)
             else:
                 raise
+        else:
+            return
 
 
 def _download_file(
@@ -131,10 +133,11 @@ def _download_file(
     # Strip specified number of directory levels
     path_parts = url_path.split("/")
     if strip_levels >= len(path_parts):
-        raise ValueError(
+        msg = (
             f"Cannot strip {strip_levels} levels from path with only "
             f"{len(path_parts)} parts: {url_path}"
         )
+        raise ValueError(msg)
 
     stripped_path = "/".join(path_parts[strip_levels:])
     destination = save_directory / stripped_path
@@ -151,7 +154,7 @@ def _download_file(
 
     # Write file with progress bar
     with (
-        open(destination, "wb") as f,
+        Path(destination).open("wb") as f,
         tqdm(
             total=total_size,
             unit="B",
@@ -218,17 +221,16 @@ def fetch_trace_data(
 
     # Validate inputs
     if dataset_type not in ["full", "example"]:
-        raise ValueError(
-            f"dataset_type must be 'full' or 'example', got: {dataset_type}"
-        )
+        msg = f"dataset_type must be 'full' or 'example', got: {dataset_type}"
+        raise ValueError(msg)
 
     if dataset_src != "isp_2024":
-        raise ValueError(f"Only isp_2024 is currently supported, got: {dataset_src}")
+        msg = f"Only isp_2024 is currently supported, got: {dataset_src}"
+        raise ValueError(msg)
 
     if data_format not in ["processed", "archive"]:
-        raise ValueError(
-            f"data_format must be 'processed' or 'archive', got: {data_format}"
-        )
+        msg = f"data_format must be 'processed' or 'archive', got: {data_format}"
+        raise ValueError(msg)
 
     # Construct manifest name and download
     manifest_name = f"{data_format}/{dataset_type}_{dataset_src}"
diff --git a/src/isp_trace_parser/resource_trace_metadata.py b/src/isp_trace_parser/resource_trace_metadata.py
index f5ffa95..8cedc7a 100644
--- a/src/isp_trace_parser/resource_trace_metadata.py
+++ b/src/isp_trace_parser/resource_trace_metadata.py
@@ -40,7 +40,8 @@ def build(
     for path in files:
         stem, sep, ref = path.stem.rpartition("_RefYear")
         if not sep or not ref.isdigit() or stem not in resource_mapping:
-            raise ValueError(f"Unexpected trace filename: {path.name}")
+            msg = f"Unexpected trace filename: {path.name}"
+            raise ValueError(msg)
         entry = resource_mapping[stem]
         file_metadata[path] = {
             "name": entry["location"],
diff --git a/src/isp_trace_parser/solar_traces.py b/src/isp_trace_parser/solar_traces.py
index aa8dbde..f858fdb 100644
--- a/src/isp_trace_parser/solar_traces.py
+++ b/src/isp_trace_parser/solar_traces.py
@@ -8,7 +8,7 @@
 import functools
 import os
 from pathlib import Path
-from typing import Literal, Optional
+from typing import Literal
 
 from joblib import Parallel, delayed
 from pydantic import BaseModel, validate_call
@@ -56,10 +56,10 @@ class SolarMetadataFilter(BaseModel):
         reference_year: list of ints specifying reference_years
     """
 
-    name: Optional[list[str]] = None
-    file_type: Optional[list[Literal["zone", "project"]]] = None
-    resource_type: Optional[list[Literal["SAT", "FFP", "CST"]]] = None
-    reference_year: Optional[list[int]] = None
+    name: list[str] | None = None
+    file_type: list[Literal["zone", "project"]] | None = None
+    resource_type: list[Literal["SAT", "FFP", "CST"]] | None = None
+    reference_year: list[int] | None = None
 
 
 @validate_call
@@ -68,7 +68,7 @@ def parse_solar_traces(
     parsed_directory: str | Path,
     use_concurrency: bool = True,
     filters: SolarMetadataFilter | None = None,
-):
+) -> None:
     """Takes a directory with AEMO solar trace data and reformats the data, saving it to a new directory.
 
     AEMO solar trace data comes in CSVs with columns specifying the year, day, and month, and data columns
@@ -164,7 +164,7 @@ def parse_solar_traces(
     }
 
     project_and_zone_output_names, project_and_zone_input_names = zip(
-        *name_mappings.items()
+        *name_mappings.items(), strict=True
     )
 
     partial_func = functools.partial(
@@ -179,12 +179,12 @@ def parse_solar_traces(
         Parallel(n_jobs=max_workers)(
             delayed(partial_func)(save_name, old_trace_name)
             for save_name, old_trace_name in zip(
-                project_and_zone_output_names, project_and_zone_input_names
+                project_and_zone_output_names, project_and_zone_input_names, strict=True
             )
         )
     else:
         for save_name, old_trace_name in zip(
-            project_and_zone_output_names, project_and_zone_input_names
+            project_and_zone_output_names, project_and_zone_input_names, strict=True
         ):
             partial_func(save_name, old_trace_name)
 
@@ -283,7 +283,7 @@ def get_unique_resource_types_in_metadata(
         A list of unique resource types.
     """
     return list(
-        set(metadata["resource_type"] for metadata in metadata_for_trace_files.values())
+        {metadata["resource_type"] for metadata in metadata_for_trace_files.values()}
     )
 
 
diff --git a/src/isp_trace_parser/trace_formatter.py b/src/isp_trace_parser/trace_formatter.py
index c889520..c9ec713 100644
--- a/src/isp_trace_parser/trace_formatter.py
+++ b/src/isp_trace_parser/trace_formatter.py
@@ -72,10 +72,10 @@ def trace_formatter(trace_data: pl.DataFrame) -> pl.DataFrame:
         value_name="value",
     )
 
-    def get_hour(time_label):
+    def get_hour(time_label: str) -> timedelta:
         return timedelta(hours=int(time_label) // 2)
 
-    def get_minute(time_label):
+    def get_minute(time_label: str) -> timedelta:
         return timedelta(minutes=int(time_label) % 2 * 30)
 
     trace_data = trace_data.with_columns(
diff --git a/src/isp_trace_parser/trace_restructure_helper_functions.py b/src/isp_trace_parser/trace_restructure_helper_functions.py
index 8d9b43b..0a74dbb 100644
--- a/src/isp_trace_parser/trace_restructure_helper_functions.py
+++ b/src/isp_trace_parser/trace_restructure_helper_functions.py
@@ -5,7 +5,6 @@
 # the Free Software Foundation; either version 3 of the License, or
 # (at your option) any later version.
 
-from datetime import timedelta
 from pathlib import Path
 
 import polars as pl
@@ -17,14 +16,12 @@
 def get_all_filepaths(directory: Path) -> list[Path]:
     if directory.is_dir():
         return [path for path in Path(directory).rglob("*.csv") if path.is_file()]
-    else:
-        raise ValueError(f"{directory} not found.")
+    raise FileNotFoundError(directory)
 
 
 def read_trace_csv(file: Path) -> pl.DataFrame:
     pl_types = [pl.Int64] * 3 + [pl.Float64] * 48
-    data = pl.read_csv(file, schema_overrides=pl_types)
-    return data
+    return pl.read_csv(file, schema_overrides=pl_types)
 
 
 def read_and_format_traces(files: list[Path]) -> list[pl.DataFrame]:
@@ -38,10 +35,9 @@ def read_and_format_traces(files: list[Path]) -> list[pl.DataFrame]:
 
 def calculate_average_trace(traces: list[pl.DataFrame]) -> pl.DataFrame:
     combined_traces = pl.concat(traces)
-    average_trace = combined_traces.group_by("datetime").agg(
+    return combined_traces.group_by("datetime").agg(
         [pl.col("value").mean().alias("value")]
     )
-    return average_trace
 
 
 def _frame_with_metadata(trace: pl.DataFrame, file_metadata: dict) -> pl.DataFrame:
@@ -79,11 +75,7 @@ def process_and_save_files(
 ) -> None:
     traces = read_and_format_traces(files)
 
-    if len(traces) > 1:
-        trace = calculate_average_trace(traces)
-    else:
-        trace = traces[0]
-
+    trace = calculate_average_trace(traces) if len(traces) > 1 else traces[0]
     trace = _frame_with_metadata(trace, file_metadata)
 
     save_trace(trace, file_metadata, output_directory, write_output_filepath)
@@ -94,21 +86,18 @@ def get_metadata_that_matches_trace_names(
 ) -> dict[Path, dict[str, str]]:
     if isinstance(trace_names, str):
         trace_names = [trace_names]
-    matching_meta_data = {
+    return {
         f: metadata.copy()
         for f, metadata in all_input_file_metadata.items()
         if metadata["name"] in trace_names
     }
-    return matching_meta_data
 
 
 def get_unique_reference_years_in_metadata(
     metadata_for_trace_files: dict[Path, dict[str, str]],
 ) -> list[str]:
     return list(
-        set(
-            metadata["reference_year"] for metadata in metadata_for_trace_files.values()
-        )
+        {metadata["reference_year"] for metadata in metadata_for_trace_files.values()}
     )
 
 
@@ -142,9 +131,12 @@ def check_filter_by_metadata(
         return True
 
     for field, allowed_values in filters.model_dump(exclude_unset=True).items():
-        if field in metadata and allowed_values is not None:
-            if metadata[field] not in allowed_values:
-                return False
+        if (
+            field in metadata
+            and allowed_values is not None
+            and metadata[field] not in allowed_values
+        ):
+            return False
 
     return True
 
@@ -152,9 +144,7 @@ def check_filter_by_metadata(
 def get_unique_project_and_zone_names_in_input_files(
     metadata_for_trace_files: dict[Path, dict[str, str]],
 ) -> list[str]:
-    names = []
-    for filepath, meta_data in metadata_for_trace_files.items():
-        names.append(meta_data["name"])
+    names = [meta_data["name"] for meta_data in metadata_for_trace_files.values()]
     return list(set(names))
 
 
@@ -172,5 +162,5 @@ def filter_mapping_by_names_in_input_files(
     return filtered_mapping
 
 
-def get_just_filepaths(metadata_for_files):
+def get_just_filepaths(metadata_for_files: dict) -> list:
     return [file for file, metadata in metadata_for_files.items()]
diff --git a/src/isp_trace_parser/wind_traces.py b/src/isp_trace_parser/wind_traces.py
index 8c3d2b7..2ff7467 100644
--- a/src/isp_trace_parser/wind_traces.py
+++ b/src/isp_trace_parser/wind_traces.py
@@ -8,7 +8,7 @@
 import functools
 import os
 from pathlib import Path
-from typing import Literal, Optional
+from typing import Literal
 
 from joblib import Parallel, delayed
 from pydantic import BaseModel, validate_call
@@ -56,10 +56,10 @@ class WindMetadataFilter(BaseModel):
         reference_year: list of ints specifying reference_years
     """
 
-    name: Optional[list[str]] = None
-    file_type: Optional[list[Literal["zone", "project"]]] = None
-    resource_type: Optional[list[Literal["WH", "WM", "WL", "WX", "wind"]]] = None
-    reference_year: Optional[list[int]] = None
+    name: list[str] | None = None
+    file_type: list[Literal["zone", "project"]] | None = None
+    resource_type: list[Literal["WH", "WM", "WL", "WX", "wind"]] | None = None
+    reference_year: list[int] | None = None
 
 
 @validate_call
@@ -68,7 +68,7 @@ def parse_wind_traces(
     parsed_directory: str | Path,
     use_concurrency: bool = True,
     filters: WindMetadataFilter | None = None,
-):
+) -> None:
     """Takes a directory with AEMO wind trace data and reformats the data, saving it to a new directory.
 
     AEMO wind trace data comes in CSVs with columns specifying the year, day, and month, and data columns
@@ -163,12 +163,14 @@ def parse_wind_traces(
     zone_name_mappings = filter_mapping_by_names_in_input_files(
         zone_name_mappings, project_and_zone_input_names
     )
-    zone_output_names, zone_input_names = zip(*zone_name_mappings.items())
+    zone_output_names, zone_input_names = zip(*zone_name_mappings.items(), strict=True)
 
     project_name_mappings = filter_mapping_by_names_in_input_files(
         project_name_mappings, project_and_zone_input_names
     )
-    project_output_names, project_input_names = zip(*project_name_mappings.items())
+    project_output_names, project_input_names = zip(
+        *project_name_mappings.items(), strict=True
+    )
 
     zone_partial_func = functools.partial(
         restructure_wind_zone_files,
@@ -189,21 +191,27 @@ def parse_wind_traces(
 
         Parallel(n_jobs=max_workers)(
             delayed(zone_partial_func)(save_name, old_trace_name)
-            for save_name, old_trace_name in zip(zone_output_names, zone_input_names)
+            for save_name, old_trace_name in zip(
+                zone_output_names, zone_input_names, strict=True
+            )
         )
 
         Parallel(n_jobs=max_workers)(
             delayed(project_partial_func)(save_name, old_trace_name)
             for save_name, old_trace_name in zip(
-                project_output_names, project_input_names
+                project_output_names, project_input_names, strict=True
             )
         )
 
     else:
-        for save_name, old_trace_name in zip(zone_output_names, zone_input_names):
+        for save_name, old_trace_name in zip(
+            zone_output_names, zone_input_names, strict=True
+        ):
             zone_partial_func(save_name, old_trace_name)
 
-        for save_name, old_trace_name in zip(project_output_names, project_input_names):
+        for save_name, old_trace_name in zip(
+            project_output_names, project_input_names, strict=True
+        ):
             project_partial_func(save_name, old_trace_name)
 
 
@@ -330,7 +338,7 @@ def get_unique_resource_types_in_metadata(
     metadata_for_trace_files: dict[str:str],
 ) -> list:
     return list(
-        set(metadata["resource_type"] for metadata in metadata_for_trace_files.values())
+        {metadata["resource_type"] for metadata in metadata_for_trace_files.values()}
     )
 
 
diff --git a/tests/conftest.py b/tests/conftest.py
index 8275ad8..04285b3 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -16,7 +16,7 @@
 
 
 @pytest.fixture(params=[True, False], ids=["concurrent", "sequential"], scope="module")
-def parsed_trace_trace_directory(request):
+def parsed_trace_trace_directory(request) -> Path:
     """Fixture that performs parsing of wind and solar trace directory once, providing
     the output directory to multiple test cases that validate different files.
 
@@ -59,7 +59,7 @@ def parsed_trace_trace_directory(request):
 
         optimise_parquet.partition_traces_by_columns(
             input_directory=tmp_parsed_directory / "demand",
-            output_directory=tmp_parsed_directory / f"demand_optimised",
+            output_directory=tmp_parsed_directory / "demand_optimised",
             partition_cols=["scenario", "reference_year"],
         )
         yield tmp_parsed_directory
diff --git a/tests/create_end_to_end_test_data.py b/tests/create_end_to_end_test_data.py
index 5bf3ed6..e45e95f 100644
--- a/tests/create_end_to_end_test_data.py
+++ b/tests/create_end_to_end_test_data.py
@@ -13,7 +13,7 @@
 import pandas as pd
 
 
-def generate_random_data(start_year, end_year):
+def generate_random_data(start_year: int, end_year: int) -> pd.DataFrame:
     # Generate date range from July 1st of the start year to July 1st of the end year (excluding end)
     date_range = pd.date_range(
         start=f"{start_year}-01-01", end=f"{end_year}-01-01", freq="D", inclusive="left"
@@ -31,14 +31,13 @@ def generate_random_data(start_year, end_year):
     half_hour_columns = [f"{i:02d}" for i in range(1, 49)]
 
     # Combine the date components with the random data
-    df = pd.concat([df, pd.DataFrame(random_data, columns=half_hour_columns)], axis=1)
-    return df
+    return pd.concat([df, pd.DataFrame(random_data, columns=half_hour_columns)], axis=1)
 
 
 data = generate_random_data(start_year=config.start, end_year=config.end)
 
 
-def simple_flatten(nested_list):
+def simple_flatten(nested_list: list) -> list:
     flattened = []
     for item in nested_list:
         if isinstance(item, list):
@@ -48,7 +47,7 @@ def simple_flatten(nested_list):
     return flattened
 
 
-def create_solar_csvs(directory):
+def create_solar_csvs(directory: Path) -> None:
     combos = itertools.product(config.reference_years, config.solar_projects)
     for y, project in combos:
         data.to_csv(directory / Path(f"{project}_FFP_RefYear{y}.csv"), index=False)
@@ -60,7 +59,7 @@ def create_solar_csvs(directory):
         )
 
 
-def create_wind_csvs(directory):
+def create_wind_csvs(directory: Path) -> None:
     combos = itertools.product(
         config.reference_years, simple_flatten(config.wind_projects.values())
     )
@@ -78,7 +77,7 @@ def create_wind_csvs(directory):
         )
 
 
-def create_demand_csvs(directory):
+def create_demand_csvs(directory: Path) -> None:
     combos = itertools.product(
         config.reference_years,
         config.sub_regions,
diff --git a/tests/test_demand_trace_metadata.py b/tests/test_demand_trace_metadata.py
index 22414e2..8c48ae4 100644
--- a/tests/test_demand_trace_metadata.py
+++ b/tests/test_demand_trace_metadata.py
@@ -12,7 +12,7 @@
 from isp_trace_parser import demand_trace_metadata
 
 
-def test_build():
+def test_build() -> None:
     """Two examples spanning different scenario / poe / demand_type /
     subregion values. Every combination resolves through the same single
     dict lookup, so two are enough for testing.
@@ -47,6 +47,6 @@ def test_build():
         "VIC_RefYear_2011_MYSTERY_POE10_OPSO_MODELLING.csv",  # lookup miss
     ],
 )
-def test_build_rejects_unexpected_filename(filename):
+def test_build_rejects_unexpected_filename(filename: str) -> None:
     with pytest.raises(ValueError, match="Unexpected trace filename"):
         demand_trace_metadata.build([Path(filename)], version="2024")
diff --git a/tests/test_download.py b/tests/test_download.py
index 7c8bed0..4edbd89 100644
--- a/tests/test_download.py
+++ b/tests/test_download.py
@@ -16,7 +16,7 @@
 TEST_EXPECTED_CONTENT = b"ISP Trace Parser Test File\n"
 
 
-def test_download_test_file():
+def test_download_test_file() -> None:
     """Test download with actual server file."""
 
     with TemporaryDirectory() as tmp_path:
@@ -28,7 +28,7 @@ def test_download_test_file():
         assert downloaded.read_bytes() == TEST_EXPECTED_CONTENT
 
 
-def test_download_with_retry():
+def test_download_with_retry() -> None:
     """Test retry logic with real server."""
 
     with TemporaryDirectory() as tmp_path:
@@ -38,7 +38,7 @@ def test_download_with_retry():
         assert (tmp_path / "test" / "test" / "test_file.txt").exists()
 
 
-def test_fetch_trace_data_with_test_manifest(monkeypatch):
+def test_fetch_trace_data_with_test_manifest(monkeypatch: pytest.MonkeyPatch) -> None:
     """Test downloading from a small, test manifest.
     The testing manifest, while still named "full_isp_2024" here, is just a test manifest
     with containing a single url ("https://data.openisp.au/test/test/test_file.txt")
@@ -48,7 +48,7 @@ def test_fetch_trace_data_with_test_manifest(monkeypatch):
         tmp_path = Path(tmp_path)
 
         # Point to test fixtures instead of production manifests
-        def mock_files(package):
+        def mock_files(package) -> Path:
             return Path(__file__).parent / "fixtures" / "manifests"
 
         monkeypatch.setattr("isp_trace_parser.remote.download.files", mock_files)
@@ -65,7 +65,7 @@ def mock_files(package):
         assert downloaded.read_bytes() == TEST_EXPECTED_CONTENT
 
 
-def test_manifest_not_found():
+def test_manifest_not_found() -> None:
     """Test downloading from a small, test manifest."""
 
     with pytest.raises(FileNotFoundError):
@@ -75,7 +75,7 @@ def test_manifest_not_found():
 
 
 @pytest.mark.parametrize("unquote", [True, False])
-def test_fetch_trace_data(unquote: bool, monkeypatch):
+def test_fetch_trace_data(unquote: bool, monkeypatch: pytest.MonkeyPatch) -> None:
     """Test downloading via fetch_trace_data with test fixtures.
     This, while still download a dataset name "full", is just a pointing to a test manifest
     manifest with containing a single url ("https://data.openisp.au/test/test/test_file.txt")
@@ -85,7 +85,7 @@ def test_fetch_trace_data(unquote: bool, monkeypatch):
         tmp_path = Path(tmp_path)
 
         # Point to test manifests instead of production manifests
-        def mock_files(package):
+        def mock_files(package) -> Path:
             return Path(__file__).parent / "fixtures" / "manifests"
 
         monkeypatch.setattr("isp_trace_parser.remote.download.files", mock_files)
@@ -102,13 +102,13 @@ def mock_files(package):
         assert downloaded.read_bytes() == TEST_EXPECTED_CONTENT
 
 
-def test_wrong_source():
+def test_wrong_source() -> None:
     # no ISP 2025 data
     with pytest.raises(ValueError, match="Only isp_2024 is currently supported"):
         download.fetch_trace_data("example", "isp_2025", "/", "archive")
 
 
-def test_wrong_format():
+def test_wrong_format() -> None:
     # only archive or processed data (not other)
     with pytest.raises(
         ValueError, match="data_format must be 'processed' or 'archive'"
@@ -116,21 +116,19 @@ def test_wrong_format():
         download.fetch_trace_data("example", "isp_2024", "/", "other")
 
 
-def test_wrong_type():
+def test_wrong_type() -> None:
     # only full or example type
     with pytest.raises(ValueError):
         download.fetch_trace_data("other", "isp_2024", "/", "archive")
 
 
-def test_empty_manifest(monkeypatch):
+def test_empty_manifest(monkeypatch: pytest.MonkeyPatch) -> None:
     """Test that empty manifest raises ValueError."""
-    from importlib.resources import files
-
     with TemporaryDirectory() as tmp_path:
         tmp_path = Path(tmp_path)
 
         # Point to test manifest instead of production manifests
-        def mock_files(package):
+        def mock_files(package) -> Path:
             return Path(__file__).parent / "fixtures" / "manifests"
 
         monkeypatch.setattr("isp_trace_parser.remote.download.files", mock_files)
@@ -139,7 +137,7 @@ def mock_files(package):
             download._download_from_manifest("empty_manifest", tmp_path, strip_levels=0)
 
 
-def test_strip_levels_too_high():
+def test_strip_levels_too_high() -> None:
     """Test that strip_levels >= path parts raises ValueError."""
     with TemporaryDirectory() as tmp_path:
         tmp_path = Path(tmp_path)
diff --git a/tests/test_get_data.py b/tests/test_get_data.py
index 3f454d3..44637d4 100644
--- a/tests/test_get_data.py
+++ b/tests/test_get_data.py
@@ -32,7 +32,7 @@
 TEST_DATA = Path(__file__).parent / "test_data"
 
 
-def test_year_range_to_dt_range_fy():
+def test_year_range_to_dt_range_fy() -> None:
     """Test financial year conversion."""
     start_dt, end_dt = _year_range_to_dt_range(2022, 2024, year_type="fy")
 
@@ -40,7 +40,7 @@ def test_year_range_to_dt_range_fy():
     assert end_dt == datetime.datetime(2024, 7, 1, 0, 0)
 
 
-def test_year_range_to_dt_range_calendar():
+def test_year_range_to_dt_range_calendar() -> None:
     """Test calendar year conversion."""
     start_dt, end_dt = _year_range_to_dt_range(2022, 2024, year_type="calendar")
 
@@ -49,7 +49,9 @@ def test_year_range_to_dt_range_calendar():
 
 
 @pytest.mark.parametrize("year_type", ["fy", "calendar"])
-def test_get_zone_single_reference_year(parsed_trace_trace_directory: Path, year_type):
+def test_get_zone_single_reference_year(
+    parsed_trace_trace_directory: Path, year_type: str
+) -> None:
     test_df_lazy = pl.scan_parquet(TEST_DATA / "output" / "RefYear2022_N2_CST.parquet")
 
     start_dt, end_dt = _year_range_to_dt_range(2023, 2024, year_type=year_type)
@@ -76,7 +78,7 @@ def test_get_zone_single_reference_year(parsed_trace_trace_directory: Path, year
     pd.testing.assert_frame_equal(test_df, df)
 
 
-def test_get_zone_multiple_reference_year(parsed_trace_trace_directory: Path):
+def test_get_zone_multiple_reference_year(parsed_trace_trace_directory: Path) -> None:
     test_df_lazy = pl.scan_parquet(TEST_DATA / "output" / "RefYear2022_N1_WM.parquet")
 
     test_df = (
@@ -100,7 +102,7 @@ def test_get_zone_multiple_reference_year(parsed_trace_trace_directory: Path):
     pd.testing.assert_frame_equal(test_df, df)
 
 
-def test_get_project_single_reference_year(parsed_trace_trace_directory: Path):
+def test_get_project_single_reference_year(parsed_trace_trace_directory: Path) -> None:
     test_df_lazy = pl.scan_parquet(
         TEST_DATA / "output" / "RefYear2022_Bodangora_Wind_Farm.parquet"
     )
@@ -127,7 +129,9 @@ def test_get_project_single_reference_year(parsed_trace_trace_directory: Path):
     pd.testing.assert_frame_equal(test_df, df)
 
 
-def test_get_project_multiple_reference_year(parsed_trace_trace_directory: Path):
+def test_get_project_multiple_reference_year(
+    parsed_trace_trace_directory: Path,
+) -> None:
     test_df_lazy = pl.scan_parquet(
         TEST_DATA / "output" / "RefYear2022_Broken_Hill_Solar_Farm_FFP.parquet"
     )
@@ -152,7 +156,7 @@ def test_get_project_multiple_reference_year(parsed_trace_trace_directory: Path)
     pd.testing.assert_frame_equal(test_df, df)
 
 
-def test_get_demand_single_reference_year(parsed_trace_trace_directory: Path):
+def test_get_demand_single_reference_year(parsed_trace_trace_directory: Path) -> None:
     test_df_lazy = pl.scan_parquet(
         TEST_DATA
         / "output"
@@ -185,7 +189,7 @@ def test_get_demand_single_reference_year(parsed_trace_trace_directory: Path):
     pd.testing.assert_frame_equal(test_df, df)
 
 
-def test_get_demand_multiple_reference_year(parsed_trace_trace_directory: Path):
+def test_get_demand_multiple_reference_year(parsed_trace_trace_directory: Path) -> None:
     test_df_lazy = pl.scan_parquet(
         TEST_DATA
         / "output"
@@ -215,7 +219,7 @@ def test_get_demand_multiple_reference_year(parsed_trace_trace_directory: Path):
     pd.testing.assert_frame_equal(test_df, df)
 
 
-def test_explicit_select_columns(parsed_trace_trace_directory):
+def test_explicit_select_columns(parsed_trace_trace_directory: Path) -> None:
     df = get_zone_single_reference_year(
         start_year=2023,
         end_year=2024,
@@ -228,7 +232,7 @@ def test_explicit_select_columns(parsed_trace_trace_directory):
     assert list(df.columns) == ["datetime", "value", "zone"]
 
 
-def test_multi_value_filter(parsed_trace_trace_directory):
+def test_multi_value_filter(parsed_trace_trace_directory: Path) -> None:
     df = get_zone_single_reference_year(
         start_year=2023,
         end_year=2024,
@@ -241,7 +245,7 @@ def test_multi_value_filter(parsed_trace_trace_directory):
     assert "zone" in df.columns
 
 
-def test_wind_project_single_reference_year(parsed_trace_trace_directory):
+def test_wind_project_single_reference_year(parsed_trace_trace_directory: Path) -> None:
     test_df_lazy = pl.scan_parquet(
         TEST_DATA / "output" / "RefYear2022_Bodangora_Wind_Farm.parquet"
     )
@@ -267,7 +271,9 @@ def test_wind_project_single_reference_year(parsed_trace_trace_directory):
     pd.testing.assert_frame_equal(test_df, df)
 
 
-def test_solar_project_single_reference_year(parsed_trace_trace_directory):
+def test_solar_project_single_reference_year(
+    parsed_trace_trace_directory: Path,
+) -> None:
     test_df_lazy = pl.scan_parquet(
         TEST_DATA / "output" / "RefYear2022_Broken_Hill_Solar_Farm_FFP.parquet"
     )
@@ -293,7 +299,9 @@ def test_solar_project_single_reference_year(parsed_trace_trace_directory):
     pd.testing.assert_frame_equal(test_df, df)
 
 
-def test_solar_project_multiple_reference_years(parsed_trace_trace_directory: Path):
+def test_solar_project_multiple_reference_years(
+    parsed_trace_trace_directory: Path,
+) -> None:
     test_df_lazy = pl.scan_parquet(
         TEST_DATA / "output" / "RefYear2022_Broken_Hill_Solar_Farm_FFP.parquet"
     )
@@ -318,7 +326,9 @@ def test_solar_project_multiple_reference_years(parsed_trace_trace_directory: Pa
     pd.testing.assert_frame_equal(test_df, df)
 
 
-def test_wind_project_multiple_reference_years(parsed_trace_trace_directory: Path):
+def test_wind_project_multiple_reference_years(
+    parsed_trace_trace_directory: Path,
+) -> None:
     test_df_lazy = pl.scan_parquet(
         TEST_DATA / "output" / "RefYear2022_Bodangora_Wind_Farm.parquet"
     )
@@ -343,7 +353,7 @@ def test_wind_project_multiple_reference_years(parsed_trace_trace_directory: Pat
     pd.testing.assert_frame_equal(test_df, df)
 
 
-def test_solar_area_single_reference_year(parsed_trace_trace_directory: Path):
+def test_solar_area_single_reference_year(parsed_trace_trace_directory: Path) -> None:
     test_df_lazy = pl.scan_parquet(TEST_DATA / "output" / "RefYear2022_N2_CST.parquet")
 
     start_dt, end_dt = _year_range_to_dt_range(2023, 2024, year_type="fy")
@@ -369,7 +379,7 @@ def test_solar_area_single_reference_year(parsed_trace_trace_directory: Path):
     pd.testing.assert_frame_equal(test_df, df)
 
 
-def test_demand_single_reference_year(parsed_trace_trace_directory: Path):
+def test_demand_single_reference_year(parsed_trace_trace_directory: Path) -> None:
     test_df_lazy = pl.scan_parquet(
         TEST_DATA
         / "output"
@@ -402,7 +412,7 @@ def test_demand_single_reference_year(parsed_trace_trace_directory: Path):
     pd.testing.assert_frame_equal(test_df, df)
 
 
-def test_demand_multiple_reference_years(parsed_trace_trace_directory: Path):
+def test_demand_multiple_reference_years(parsed_trace_trace_directory: Path) -> None:
     test_df_lazy = pl.scan_parquet(
         TEST_DATA
         / "output"
diff --git a/tests/test_input_validation.py b/tests/test_input_validation.py
index a631127..f0d5a3c 100644
--- a/tests/test_input_validation.py
+++ b/tests/test_input_validation.py
@@ -38,7 +38,7 @@
         },
     ],
 )
-def test_solar_metadata_filter_valid(valid_input):
+def test_solar_metadata_filter_valid(valid_input: dict[str, list]) -> None:
     assert SolarMetadataFilter(**valid_input)
 
 
@@ -51,7 +51,9 @@ def test_solar_metadata_filter_valid(valid_input):
         ({"name": 123}, "Input should be a valid list"),
     ],
 )
-def test_solar_metadata_filter_invalid(invalid_input, expected_error):
+def test_solar_metadata_filter_invalid(
+    invalid_input: dict[str, list], expected_error: str
+) -> None:
     with pytest.raises(ValidationError, match=expected_error):
         SolarMetadataFilter(**invalid_input)
 
@@ -71,7 +73,7 @@ def test_solar_metadata_filter_invalid(invalid_input, expected_error):
         },
     ],
 )
-def test_wind_metadata_filter_valid(valid_input):
+def test_wind_metadata_filter_valid(valid_input: dict[str, list]) -> None:
     assert WindMetadataFilter(**valid_input)
 
 
@@ -87,7 +89,9 @@ def test_wind_metadata_filter_valid(valid_input):
         ({"name": 123}, "Input should be a valid list"),
     ],
 )
-def test_wind_metadata_filter_invalid(invalid_input, expected_error):
+def test_wind_metadata_filter_invalid(
+    invalid_input: dict[str, list], expected_error: str
+) -> None:
     with pytest.raises(ValidationError, match=expected_error):
         WindMetadataFilter(**invalid_input)
 
@@ -109,7 +113,7 @@ def test_wind_metadata_filter_invalid(invalid_input, expected_error):
         },
     ],
 )
-def test_demand_metadata_filter_valid(valid_input):
+def test_demand_metadata_filter_valid(valid_input: dict[str, list]) -> None:
     assert DemandMetadataFilter(**valid_input)
 
 
@@ -129,7 +133,9 @@ def test_demand_metadata_filter_valid(valid_input):
         ({"subregion": 123}, "Input should be a valid list"),
     ],
 )
-def test_demand_metadata_filter_invalid(invalid_input, expected_error):
+def test_demand_metadata_filter_invalid(
+    invalid_input: dict[str, str | int | list], expected_error: str
+) -> None:
     with pytest.raises(ValidationError, match=expected_error):
         DemandMetadataFilter(**invalid_input)
 
@@ -152,7 +158,7 @@ def test_demand_metadata_filter_invalid(invalid_input, expected_error):
         },
     ],
 )
-def test_parse_traces_validation(invalid_input):
+def test_parse_traces_validation(invalid_input: dict[str, str | int | list]) -> None:
     with pytest.raises(ValidationError):
         parse_solar_traces(**invalid_input)
     with pytest.raises(ValidationError):
@@ -170,12 +176,14 @@ def test_parse_traces_validation(invalid_input):
         {"start_year": 2030, "end_year": 2035, "reference_years": [2011, "x", 2018]},
     ],
 )
-def test_construct_reference_year_mapping_validation_invalid(invalid_input):
+def test_construct_reference_year_mapping_validation_invalid(
+    invalid_input: dict,
+) -> None:
     with pytest.raises(ValidationError):
         construct_reference_year_mapping(**invalid_input)
 
 
-def test_construct_reference_year_mapping_validation_valid():
+def test_construct_reference_year_mapping_validation_valid() -> None:
     result = construct_reference_year_mapping(
         start_year=2030, end_year=2035, reference_years=[2011, 2013, 2018]
     )
@@ -185,12 +193,11 @@ def test_construct_reference_year_mapping_validation_valid():
 
 
 # Tests for custom input validation functions
-def test_input_directory(tmp_path):
+def test_input_directory(tmp_path: Path) -> None:
     valid_dir = tmp_path / "valid_dir"
     valid_dir.mkdir()
     assert input_validation.input_directory(valid_dir) == valid_dir
-
-    with pytest.raises(ValueError, match="Directory .* does not exist"):
+    with pytest.raises(FileNotFoundError):
         input_validation.input_directory(tmp_path / "non_existent_dir")
 
 
@@ -201,7 +208,7 @@ def test_input_directory(tmp_path):
         Path("/valid/path"),
     ],
 )
-def test_parsed_directory_valid(valid_path):
+def test_parsed_directory_valid(valid_path: Path | str) -> None:
     result = input_validation.parsed_directory(valid_path)
     assert isinstance(result, Path)
 
@@ -214,7 +221,7 @@ def test_parsed_directory_valid(valid_path):
         [],
     ],
 )
-def test_parsed_directory_invalid(invalid_path):
+def test_parsed_directory_invalid(invalid_path: Path | str) -> None:
     with pytest.raises(ValueError, match="Invalid parsed directory path"):
         input_validation.parsed_directory(invalid_path)
 
@@ -226,7 +233,7 @@ def test_parsed_directory_invalid(invalid_path):
         Path("/valid/path"),
     ],
 )
-def test_is_valid_path_valid(valid_path):
+def test_is_valid_path_valid(valid_path: Path | str) -> None:
     result = input_validation.is_valid_path(valid_path)
     assert isinstance(result, Path)
 
@@ -239,7 +246,7 @@ def test_is_valid_path_valid(valid_path):
         [],
     ],
 )
-def test_is_valid_path_invalid(invalid_path):
+def test_is_valid_path_invalid(invalid_path: Path | str) -> None:
     with pytest.raises(ValueError, match="Invalid parsed directory path"):
         input_validation.is_valid_path(invalid_path)
 
@@ -252,7 +259,7 @@ def test_is_valid_path_invalid(invalid_path):
         (-10, 0),
     ],
 )
-def test_start_year_before_end_year_valid(start, end):
+def test_start_year_before_end_year_valid(start: int, end: int) -> None:
     assert input_validation.start_year_before_end_year(start, end) is None
 
 
@@ -264,6 +271,6 @@ def test_start_year_before_end_year_valid(start, end):
         (2020, 2019),
     ],
 )
-def test_start_year_before_end_year_invalid(start, end):
+def test_start_year_before_end_year_invalid(start: int, end: int) -> None:
     with pytest.raises(ValueError, match="Start year .* < end year"):
         input_validation.start_year_before_end_year(start, end)
diff --git a/tests/test_optimise_parquet.py b/tests/test_optimise_parquet.py
index beec176..01c9b59 100644
--- a/tests/test_optimise_parquet.py
+++ b/tests/test_optimise_parquet.py
@@ -20,7 +20,9 @@
     "expected_data, file_type",
     [("zone_data_0.parquet", "zone"), ("project_data_0.parquet", "project")],
 )
-def test_optimisation(parsed_trace_trace_directory, expected_data, file_type):
+def test_optimisation(
+    parsed_trace_trace_directory: Path, expected_data: str, file_type: str
+) -> None:
     """Test wind trace parsing produces expected parquet outputs (both for a sample wind project and wind zone)"""
     test_output_parquet = TEST_DATA / "output" / expected_data
 
diff --git a/tests/test_resource_trace_metadata.py b/tests/test_resource_trace_metadata.py
index 61861ae..2f5c063 100644
--- a/tests/test_resource_trace_metadata.py
+++ b/tests/test_resource_trace_metadata.py
@@ -12,7 +12,7 @@
 from isp_trace_parser import resource_trace_metadata
 
 
-def test_build():
+def test_build() -> None:
     """One test covers function logic compared with regex approach
 
     Solar zones / wind zones / extra reference years add no new code-path
@@ -42,6 +42,6 @@ def test_build():
         "Mystery_Plant_RefYear2011.csv",  # stem not in mapping
     ],
 )
-def test_build_rejects_unexpected_filename(filename):
+def test_build_rejects_unexpected_filename(filename: str) -> None:
     with pytest.raises(ValueError, match="Unexpected trace filename"):
         resource_trace_metadata.build([Path(filename)], version="2024")
diff --git a/tests/test_trace_formatter.py b/tests/test_trace_formatter.py
index 90be4a6..9cb93c7 100644
--- a/tests/test_trace_formatter.py
+++ b/tests/test_trace_formatter.py
@@ -11,7 +11,7 @@
 from isp_trace_parser import trace_formatter, trace_restructure_helper_functions
 
 
-def test_trace_formatter():
+def test_trace_formatter() -> None:
     # Test trace formatting works by using formatting function works by performing formatting and then
     # reversing the formatting changes and checking the result matches the original data.
     filepath = (
diff --git a/tests/test_trace_parsers.py b/tests/test_trace_parsers.py
index a49954a..64ae3a3 100644
--- a/tests/test_trace_parsers.py
+++ b/tests/test_trace_parsers.py
@@ -12,13 +12,13 @@
 import pytest
 from polars.testing import assert_frame_equal
 
-from isp_trace_parser import demand_traces, solar_traces, wind_traces
+from isp_trace_parser import demand_traces
 
 TEST_DATA = Path(__file__).parent / "test_data"
 
 
 @pytest.mark.parametrize("use_concurrency", [True, False])
-def test_demand_trace_parsing(use_concurrency: bool):
+def test_demand_trace_parsing(use_concurrency: bool) -> None:
     """Test demand trace parsing produces expected parquet output."""
     test_demand_csv_directory = TEST_DATA / "demand"
     expected_filename = "CNSW_RefYear_2011_HYDROGEN_EXPORT_POE10_OPSO_MODELLING.parquet"
@@ -50,7 +50,9 @@ def test_demand_trace_parsing(use_concurrency: bool):
         ("RefYear2022_N1_WM.parquet", "zone"),
     ],
 )
-def test_wind_trace_parsing(parsed_trace_trace_directory, expected_filename, file_type):
+def test_wind_trace_parsing(
+    parsed_trace_trace_directory: Path, expected_filename: str, file_type: str
+) -> None:
     """Test wind trace parsing produces expected parquet outputs (both for a sample wind project and wind zone)"""
     test_output_parquet = TEST_DATA / "output" / expected_filename
 
@@ -70,8 +72,8 @@ def test_wind_trace_parsing(parsed_trace_trace_directory, expected_filename, fil
     ],
 )
 def test_solar_trace_parsing(
-    parsed_trace_trace_directory, expected_filename, file_type
-):
+    parsed_trace_trace_directory: Path, expected_filename: str, file_type: str
+) -> None:
     """Test solar trace parsing produces expected parquet output (both for a sample solar project and solar zone)"""
     test_output_parquet = TEST_DATA / "output" / expected_filename
 
diff --git a/tests/test_writing_save_names.py b/tests/test_writing_save_names.py
index 36e3c30..ffd3be3 100644
--- a/tests/test_writing_save_names.py
+++ b/tests/test_writing_save_names.py
@@ -8,7 +8,7 @@
 import isp_trace_parser
 
 
-def test_write_solar_save_names():
+def test_write_solar_save_names() -> None:
     meta_data = {
         "name": "a",
         "reference_year": "1",
@@ -32,7 +32,7 @@ def test_write_solar_save_names():
     assert str(save_filepath) == "RefYear1_a_x.parquet"
 
 
-def test_write_wind_save_names():
+def test_write_wind_save_names() -> None:
     meta_data = {
         "name": "a",
         "reference_year": "1",