MRDown

English | 日本語

A Markdown viewer at heart — it edits, saves, and creates too, and the diff is the showpiece.

It began with the .md files Claude Code generates. Opening a heavy editor and right-clicking to preview was a chore — so I asked Claude Code for help and had a viewer-only 0.1 in two hours. At first it was a split — write in an editor, read in MRDown. That split is gone: I no longer open VSCode for .md at all, I read and write here. From there, one "it'd be nice if it also…" after another, it grew — until it did something no other Markdown app does: read the diff of what your AI just rewrote.

Built with Tauri + TypeScript. Only macOS builds are published, but it is not macOS-only — being Tauri, it should build and run on Windows. I have never built or launched it there myself, and there is no Windows code-signing certificate, so no Windows binary is distributed.

Features

• History and diffs: every save — and every rewrite from outside the app — quietly keeps a timestamped version. The History panel (clock icon) puts any two versions side by side so you can read what changed (only the words that differ are marked; unchanged runs are folded away). In a Git repository, HEAD joins the same list, so the diff against what's committed is right there. Restore any version into the editor in one click, non-destructively (nothing is written until you save). Versions live in the app's data directory, so they never clutter your files or Git repos. Git is optional.
• Compare any two files (⌘⇧D): File ▸ "Compare Two Files…" — pick two, and read the difference in exactly the same view the version timeline uses. Works with nothing open.
• Nothing is lost when an agent rewrites the file under you: if something changes the file on disk while you have unsaved edits, MRDown neither overwrites it silently nor reloads over you. The disk's version is snapshotted the moment it's seen, and your unsaved edits are snapshotted before they're discarded. Three columns — last save, what's on disk, your edits — with only the lines you both rewrote differently marked as conflicts. Versions record where they came from (saved / changed elsewhere / back to the committed version / rescued draft). Which application wrote a file isn't knowable — macOS doesn't record it — except for Git: content matching the committed blob byte-for-byte was Git putting the file back.
• Document header. Put a title, document number, version, date, author or confidentiality marking in the frontmatter and they are drawn as a band at the top of the document (the keys work in either language — title or タイトル). A logo is registered once in Settings ▸ Document header and appears on every document that has one. What you see in the preview is what lands in the PDF. The band is drawn once, at the top: a preview has no pages, so repeating it per printed page would make the screen and the output disagree. For the same reason there are no page numbers — the CSS mechanism for them isn't implemented by the browser engine, so it isn't ours to control.
• Any other YAML frontmatter is still shown as a tidy collapsed metadata card, instead of leaking tags: lines into the body.
• Templates, so you don't start from a blank page. ⌘N still lands you on an empty document instantly — the design-doc and spec templates simply float in the space that empty page leaves. Click one and the skeleton drops in; start typing and they disappear, so wanting a blank sheet costs you nothing. The two that ship are skeletons: headings, empty tables and a one-line prompt per section, with no prose (a filled-in template only gets in the way of an organisation whose format differs).
• Bring your own templates. A template is just a .md file in a folder — no bespoke format, no management screen (to change one, open that .md and edit it). Keeping them inside a repository is the recommended home (docs/_templates/), and Settings ▸ Templates will create them there in the folder you have open. A docs/_templates/ in the open folder is picked up automatically, so moving between repositories moves the templates with you; a setting can point elsewhere if you'd rather. Anywhere you write {{date}} becomes the date the document is created. In a repository they arrive with the clone for everyone on the team, and one line in AGENTS.md gets an AI agent writing in your format — Settings will copy that line out for you to paste.
• Take the shape of a document you liked. File ▸ Make a Template from This Document keeps the headings, table headers, frontmatter keys, comments and checklists, and drops the prose and the table contents. The result is saved nowhere — it opens as a new document. Whether the line under a heading is that section's instructions or its content isn't something a machine can decide, so the judgement stays with you and a wrong guess costs one undo.
• Open and render Markdown files (.md, .markdown, .txt).
• Drop a Word document (.docx) too — it opens as Markdown. The conversion happens on your machine and nothing is uploaded. What opens is an untitled document, so saving writes a new .md and never touches the original .docx. Images are not carried over (text, headings, lists and tables are). Feed two .docx files to Compare and you get the diff between two versions of a document.
• Create a new document (⌘N) and save it anywhere via a save dialog; an untitled doc's first # heading is offered as the file name.
• Delete the current file to the system Trash (⌘⌫ or the trash button), with a confirmation — recoverable from the Trash if it was a mistake.
• ⌘E starts editing: the preview becomes the editor in place, and ⌘E turns it back. The swap keeps the paragraph you were reading, so you read and write at the window's full width. Settings (⌘,) ▸ Appearance ▸ "Editing layout" switches to side by side instead (editor + live preview, drag the divider to resize). Settings ▸ Text width caps the source column in the swap too, so on a wide display one setting gives reading and writing the same measure. Save with ⌘S, or "Save As…" (⌘⇧S) to write a copy elsewhere.
• The editor reads as the document while you write it: headings are big, bold is bold, and markup like # or ``` is hidden — checklists become clickable checkboxes, images render where they sit, and tables are drawn with ruled borders. The line the caret is on always shows its raw markup, so the Markdown is one keystroke away. The buffer stays plain text throughout, so saving never rewrites a byte of your file — which is what keeps the diff above honest.
• Find & replace in the current document (⌘F): while editing it searches the source and highlights every hit (the current one emphasized); in preview it searches the rendered text so matches can span inline formatting (e.g. across **bold**). Regex, case-sensitive and whole-word toggles (remembered); step with Enter / ⇧Enter; replace one or all while editing (undoable with ⌘Z).
• Search across every open document (⌘⇧F, or the 🔍 button ▸ "Search across open documents"): one field searches the whole set you have open, matching all your words on the same line whatever their order. Results are grouped by document, each with its line number and the line quoted; pick one and that document opens in the editor with the match selected. Whatever is in the ⌘F box carries over, so ⌘F → ⌘⇧F widens the same query to every open document.
• Formatting toolbar above the editor: bold (⌘B), italic (⌘I), heading, list, quote, link, and more — each toggles/inserts the Markdown syntax around the selection (undoable with ⌘Z).
• Typing niceties: Enter continues a list (ordered items renumber, task items start unchecked, Enter on an empty item exits), Tab / ⇧Tab indent, and [, (, ` auto-close — wrapping the selection when there is one. All undoable with ⌘Z.
• Insert blocks with /: type / at the start of an empty line for a menu — table, checklist, code block, horizontal rule — filtered as you type, chosen with ↑/↓, inserted with Enter, dismissed with Esc. A / inside a line stays a path, so writing src/ is unaffected. Under a list the menu adds bullets → table; under a table, table → mermaid Gantt — each offered only where it applies. The conversion keeps the table and writes the chart below it; run it again and that chart is replaced rather than stacked.
• Paste a URL over selected text to turn it into a link ([selection](url)); paste an image to save it beside the document in assets/ and insert the ![]() for it.
• A status bar along the bottom of the window carries the document's own details — the full path (~-shortened, with a dot when there are unsaved edits), character count and estimated reading time (CJK counted per character, space-delimited text by words) — leaving the toolbar to actions alone. While editing, the editor and preview scroll in sync.
• A keyboard shortcut sheet (Help ▸ Keyboard Shortcuts, ⌘/): every shortcut on one page, including the ones no menu shows — ⌘B, ⌥↑/⌥↓ to jump between changes, ⌘↑/⌘↓ to reorder documents.
• Reading mode (⌘⇧M): hides the toolbar, sidebar and outline and centres the text, for reading a generated .md with nothing else on screen. Escape brings the chrome back.
• Pick a preview theme in Settings (⌘,): the default MRDown look, or GitHub Light / GitHub Dark for a document that reads exactly as it will on GitHub.
• Customise the toolbar in Settings (⌘,): turn any of the 14 Markdown actions (strikethrough, ordered/checklist, code block, image, table, horizontal rule, …) on or off; the choice is remembered.
• Japanese / English UI: follows your OS language by default and can be switched in Settings; the native menu (File / Edit / View) is localized too.
• Customise the look in Settings (⌘,): accent color (follows the macOS system accent, or a preset / any custom color), background and text colors (presets + a color picker), body font (system / serif / rounded) and size — background and text apply to the whole window, sidebar and toolbar included, not just the document.
• Keep multiple documents open in a sidebar (BBEdit-style): click to switch — or ↑/↓ once the list has focus — close with the circled × (⌘W), toggle the sidebar with ⌘1; the open set is restored on next launch.
• Put that list in the order you read it: drag a row, or move it with ⌘↑/⌘↓. ⌘-click and ⇧-click select several rows, which then drag and move as one block. The order is remembered with the session.
• Open a folder to browse its Markdown files as a set: pick files from a left-hand tree and expand/collapse subfolders; the opened folder is restored on next launch.
• Outline (table of contents) in a column of its own, to the right of the document: click a heading to jump to it, and the heading you're reading is highlighted as you scroll. Toggle it with ⌘2; it follows the document live while you edit. It's hidden by default while editing, so the text keeps its width — bring it back with ⌘2 and it stays (visibility is remembered separately for preview and edit). Settings (⌘,) can move it back into the left sidebar instead (where it stays collapsible).
• Size the side columns to your documents: drag the line between the sidebar and the document, or between the document and the outline. Double-click a line to put that column back to its default. The widths are remembered; a narrow window borrows the space back and returns it when you widen the window again.
• Never lose unsaved work: in-progress edits (and untitled documents that were never written to disk) are continuously kept as drafts and restored on next launch, so a quit or crash won't discard what you were writing.
• Open files by double-clicking or "Open With" (registered as a handler for those extensions), the button, ⌘O, or by dragging a file onto the window.
• Auto-reloads when the open file changes on disk (scroll position preserved).
• Recent files list on the start screen for quick reopening.
• Renders tables, code blocks, quotes, and local images (relative paths resolve against the file).
• Syntax-highlights fenced code blocks with highlight.js (lazy-loaded common bundle; tuned to the dark theme).
• Renders Mermaid diagrams in ```mermaid code blocks (lazy-loaded; falls back to source on syntax errors).
• Typesets maths with KaTeX ($…$ inline, $$…$$ display; a malformed formula is left as text rather than throwing). Footnotes ([^1]) render as a cross-linked section at the end, and - [ ] / - [x] task lists render as checkboxes.
• Export as HTML (⌘⇧E): save the rendered document as one self-contained file — styles, images and (when there's maths) KaTeX's fonts are all embedded, so it opens anywhere.
• Export as PDF (⌘P): opens the system print dialog — choose "Save as PDF". Printing switches to a light page with a light code palette, and keeps code blocks, tables and maths from splitting across pages.
• Links stay in the app: external links open in your browser, in-document anchors scroll, and links to local Markdown files ([text](./other.md)) open that file right in the app instead of leaving it.
• HTML output sanitized with DOMPurify and locked down with a strict CSP (safe to open untrusted files).
• Reload the current file (⌘R).

Install

Download the macOS build (Apple Silicon / Intel, macOS 10.15+) from the Releases page.

The binaries are signed and notarized with an Apple Developer ID, so they open normally once downloaded.

Development

npm install
npm run tauri dev

Build

npm run tauri build

License

MRDown itself is MIT licensed. The MRDown name and logo are not covered by that license — please rename and re-icon any fork you distribute.

The binaries bundle third-party open-source software; its inventory and copyright notices are in THIRD-PARTY-NOTICES.md, also readable from Settings (⌘,) inside the app. Regenerate it with npm run notice.

MRDown is open-core. What is in this repository is MRDown, all of it MIT, and it stays MIT. The paid features that are planned — AI explaining a diff, project-wide search, authenticated remotes like GitHub and SSH — will live in a separate repository and will not land here. CONTRIBUTING.md says exactly where the line is drawn.

Recommended IDE Setup

• VS Code + Tauri + rust-analyzer