HydroMark Review: Real Markdown Editing, Live, Inside OneNote

If you use OneNote and have ever wanted Markdown, there is now a real solution: HydroMark is a Windows desktop add-in that brings genuine Markdown editing with live (WYSIWYG) preview into OneNote itself, while you keep OneNote's notebooks, sections, sync and password-protected security.

Why it matters

OneNote has long been one of the best note apps: Microsoft-backed storage, all-device sync, and password-protected sections that most modern note apps dropped. But it never offered Markdown. HydroMark closes that gap without making you abandon OneNote.

Feature tour

Headings and lists

All six # levels render as native OneNote text, including level skips. Ordered, unordered, and deeply nested lists keep clean indentation and render in place.

Task lists, quotes and code

- [ ] becomes a real OneNote to-do checkbox whose state round-trips back to Markdown. > renders as a styled quote block with nested indentation, and fenced code blocks get syntax highlighting for dozens of languages.

Links, tables and text styles

Standard Markdown links become native OneNote hyperlinks; GFM tables with alignment render as proper OneNote tables, not images; and bold, italic, strikethrough and other inline styles all work.

Math, highlights and boxes

Inline $...$ and block $$...$$ formulas render as native OneNote equations — editable and scalable. ==highlight== marks key text, and INFO / WARNING / IMPORTANT / ERROR callout boxes make important notes stand out.

Mermaid and ZenUML diagrams

This is the headline feature. Write Mermaid — flowcharts, sequence, class, state, gantt charts, mindmaps, git graphs — and get a rendered diagram embedded in your page. Press Ctrl + Space on a rendered diagram to jump back to its Markdown source.

Slash command palette

Type / anywhere to open a searchable command palette that instantly inserts headings, lists, code blocks, boxes, formulas, tables or diagrams — the fastest way to write structured notes.

Pricing

HydroMark offers a 14-day full-feature free trial, then splits into a Basic tier with the core Markdown features and a Lifetime tier with all advanced features (LaTeX, diagrams, highlight boxes, themes).

Who should use it

• OneNote power users who want Markdown without leaving their notebooks.
• Students and academics who need editable LaTeX and structured notes.
• Developers and researchers who want Mermaid diagrams embedded inline.
• Anyone who values password-protected notes plus a modern writing experience.

Common questions

Do I have to leave OneNote to write Markdown?

No — everything stays inside OneNote. You write Markdown and watch it render in the same page.

Are diagrams editable after rendering?

You can jump back to the Markdown source with Ctrl + Space, edit, and re-render.

Which OneNote version does it support?

HydroMark targets the Windows desktop OneNote application.

Conclusion

HydroMark is the add-in that finally gives OneNote native-feeling Markdown with live preview, native equations, and complete Mermaid diagrams — at a lower price than the category. If you have ever wished OneNote had Markdown, this is worth the 14-day trial. Visit HydroMark to try it.