Add Markitdown Online to the tools directory

_tools/markitdown-online.md

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+---
+title: Markitdown Online
+category: "documents"
+description: "Convert documents, spreadsheets, images, and web pages to Markdown."
+icon: markitdown-online.png
+website: https://markitdown.tech/
+syntax:
+  - id: headings
+    available: y
+  - id: paragraphs
+    available: y
+  - id: line-breaks
+    available: y
+  - id: bold
+    available: y
+  - id: italic
+    available: y
+  - id: blockquotes
+    available: y
+  - id: ordered-lists
+    available: y
+  - id: unordered-lists
+    available: y
+  - id: code
+    available: y
+  - id: horizontal-rules
+    available: y
+  - id: links
+    available: y
+  - id: images
+    available: y
+  - id: tables
+    available: y
+  - id: fenced-code-blocks
+    available: y
+  - id: syntax-highlighting
+    available: y
+  - id: footnotes
+    available: y
+  - id: heading-ids
+    available: n
+  - id: definition-lists
+    available: n
+  - id: strikethrough
+    available: y
+  - id: task-lists
+    available: y
+  - id: emoji-cp
+    available: y
+  - id: emoji-sc
+    available: n
+  - id: highlight
+    available: n
+  - id: subscript
+    available: n
+  - id: superscript
+    available: n
+  - id: auto-url-linking
+    available: y
+  - id: disabling-auto-url
+    available: y
+  - id: html
+    available: n
+---
+
+[Markitdown Online](https://markitdown.tech/) is a browser-based converter for PDF, DOCX, PPTX, XLSX, HTML, CSV, JSON, XML, images, and public URLs. The generated Markdown can be previewed, edited, copied, or downloaded.
+
+Most supported file conversions run locally in the browser. The built-in editor previews GitHub Flavored Markdown tables, task lists, strikethrough, footnotes, and syntax-highlighted code blocks. It also supports optional math and Mermaid diagram rendering.
+
+{% include image.html file="/assets/images/tools/markitdown-online.png" alt="Markitdown Online file converter" %}
+
+{% include tool-syntax-table.html %}