iso.md

A minimal monospace markdown editor for macOS.

No cloud, no telemetry, no AI (despite the name — that's for later). Just a terminal-feeling WYSIWYG editor that opens .md files from Finder, exports clean PDFs, and gets out of your way.

Built on Tauri v2 + Milkdown. The shipped .app is ~10 MB.

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Highlights

• Live preview, Typora-style. Markdown renders inline as you type, powered by Milkdown + ProseMirror + remark (CommonMark & GFM: tables, task lists, strikethrough).
• Flip to raw markdown anytime. Toolbar toggle swaps the rendered view for an editable plain-text view of the on-disk source — frontmatter and all. Edit either way; the file round-trips byte-for-byte.
• Monospace by default, system font one click away. Toggle in the top-right toolbar.
• Grayscale UI, light/dark/auto. No blue tints, no color noise. Follows macOS appearance, or pick a mode manually.
• Tables that actually look like tables. Column widths adapt to the content on the page — numeric columns stay tight, prose columns get wider. Never narrower than the surrounding paragraphs.
• Real PDF export. ⌘E (or the toolbar button) opens a save dialog — pick a name and location, get a clean PDF.
• Finder integration. Double-click any .md file and it opens in iso.md.
• Keyboard-first. ⌘Z / ⇧⌘Z undo, ⌘= / ⌘- / ⌘0 zoom, ⌘S / ⌘O save/open, ⌘⇧D theme.
• Left-aligned, full-height, pinned to the left of your screen. Optimized for writing alongside something else (docs, browser, Figma).

Quickstart — download the built app

If you don't want to build from source, grab the latest .app from the Releases page (or ask the person who sent you this repo — they probably have a build handy), drag it to /Applications/, then:

# Make iso.md the default handler for .md files (optional)
swift -e 'import Cocoa
LSSetDefaultRoleHandlerForContentType(
  "net.daringfireball.markdown" as CFString,
  .all,
  "com.aaro.isomd" as CFString
)'

Build from source

Requires: macOS, Node 20+, pnpm, and a Rust toolchain via rustup.

# One-time toolchain setup
brew install rustup pnpm
rustup default stable
export PATH="$HOME/.cargo/bin:$PATH"

# Clone + build
git clone https://github.com/aaroi/iso-md.git
cd iso-md
pnpm install
pnpm tauri build

# Install to /Applications
cp -R src-tauri/target/release/bundle/macos/iso.md.app /Applications/

First build takes a few minutes (Rust crate compile). Subsequent builds are ~30 seconds.

Development

pnpm tauri dev      # hot-reload dev window with DevTools attached
pnpm build          # frontend type-check + Vite bundle
pnpm tauri build    # full production .app

The Tauri dev window auto-opens DevTools. In release builds, the devtools feature is enabled — right-click → Inspect to open the inspector if you need to debug.

Project layout

src/                    Frontend (TypeScript + Vite)
├── main.ts             App bootstrap, toolbar, menu, file I/O, PDF export
├── editor.ts           Milkdown setup (CommonMark, GFM, history)
├── table-sizer.ts      Content-adaptive column widths (see note below)
├── styles.css          Grayscale theme, mono/system font
└── print.css           Print-media overrides for PDF export

src-tauri/              Rust backend (Tauri v2)
├── src/lib.rs          Menu, window sizing, Finder-open events
├── tauri.conf.json     Bundle config + file association
└── capabilities/       fs & dialog permissions

Tech stack

Layer	What
Shell	Tauri v2 (Rust + WKWebView)
Editor	Milkdown (ProseMirror + remark)
Build	Vite + TypeScript
PDF	html2pdf.js
Font stack	ui-monospace, "SF Mono", Menlo, …

Permissions & security

The app uses Tauri's fine-grained permission system:

• Filesystem — read/write text files under $HOME, $DOCUMENTS, $DESKTOP, $DOWNLOADS, and $TEMP. No other paths are reachable. See src-tauri/capabilities/default.json.
• Dialog — open/save/ask dialogs (native macOS sheets).
• No network access. No analytics, no auto-update, no telemetry.

If a teammate opens a .md file outside one of those directories, the read will fail. Adjust the scope list in capabilities/default.json if you need broader access.

Note on table column widths

Getting content-adaptive columns in a ProseMirror editor is surprisingly hard:

1. CSS table-layout: auto distributes space near-evenly in WebKit, regardless of content length.
2. Setting inline styles on individual <td> / <col> elements gets wiped when ProseMirror replaces table DOM on state updates.

The working answer is to measure each cell's natural (no-wrap) text width in JS, compute per-column pixel widths (clamped to [60px, 520 + padding]), and inject them as CSS rules into a <style> element in <head>. ProseMirror doesn't manage <head>, so the rules survive its DOM churn. Tables scale up to match the prose column width if their content is narrower than the text below them.

The full logic lives in src/table-sizer.ts (about 150 lines).

License

MIT © 2026 Aaro Isosaari