HydroMark is a WYSIWYG Markdown editor add-in for Microsoft OneNote. Type Markdown naturally inside OneNote and see formatted output instantly It turns OneNote into a real technical-note workspace: code highlighting, LaTeX math, Mermaid / ZenUML diagrams, slash commands, tables, and source/rendered dual views. Plus page-width control and seamless import/export for when you do need a file. Built for developers, students, and technical writers who love OneNote but can’t live without Markdown.

I built HydroMark because I love taking notes in OneNote but can't live without Markdown. Existing tools either forced me to write elsewhere and export, or broke OneNote's native experience. HydroMark is a WYSIWYG Markdown add-in that sits right inside OneNote—type Markdown, hit Enter, and see it rendered instantly. No exports, no app switching. We also added LaTeX, Mermaid diagrams, code highlighting, and slash commands, because technical notes deserve more than bold text and bullet lists. A special mention goes to the slash commands and highlight blocks: a big part of why I built this add-in was exactly those—that's what makes note-taking feel truly modern. And this is just the start: I'll be gradually layering AI features on top over time. Let me know what you'd love to see next!

v1.1.0.0 is now live. We've added an AI Assistant that helps you generate content and run actions, plus tables now auto-expand to full width. Give it a try.

HydroMark

A New And Modern Markdown editor Addin For Microsoft OneNote

A New And Modern Markdown editor Addin For Microsoft OneNote