Status: Active development

Markdown is suddenly everywhere.

It's how we speak to machines now. It's how they speak to us.

We should make it nice!

But you already have a favorite text editor. You don't want a special tool for writing Markdown. You just need a way to preview the Markdown you're writing, marked up.

That's what Mud is for. It renders Markdown beautifully, bright or dark. It automatically reloads the document when you save it — or when Claude Code writes to it, or Codex, or whatever you use.

Mud shows you both sides of the document:

• Mark Up renders your Markdown as styled HTML — GitHub-flavored, with syntax-highlighted code.
• Mark Down shows the raw source with line numbers.

Hit Space to flip between them. Your scroll position carries over.

Mud is a Mac-assed Mac app with excellent command-line tooling. It's free and it's open source.

It does one thing — it marks up Markdown! — and it does it really well.

• GitHub-flavored Markdown with syntax-highlighted code blocks
• Raw source view with its own syntax highlighting and line numbers
• Space bar flips between views; scroll position preserved
• Four color themes — Austere, Blues, Earthy, Riot
• Bright / Dark / System lighting
• Table of contents sidebar
• Auto-reload on file change
• Find (Cmd+F)
• Print and Open in Browser
• Zoom, readable column, word wrap, and line number toggles

I wrote an overview of my current Claude Code workflow, and how Mud is a great fit for it: https://apps.josephpearson.org/mud/plan-workflows.html.

Install from Settings > Command Line to get a mud command.

mud file.md # Open a file in the app mud -u file.md # Render to HTML (mark-up view) mud -d file.md # Render to HTML (mark-down view) echo "# Hi" | mud -u # Pipe stdin to HTML mud -u --theme riot file.md # Pick a theme

Open Mud.xcodeproj in Xcode and build. Requires at least macOS Sonoma (14.0+).

Issues welcome! I have not enabled Pull Requests. Feel free to attach a Markdown plan document to an issue for any proposed fix or improvement.

• Doc/HUMANS.md — orientation guide for human beings
• Doc/AGENTS.md — architecture guide for coding agents
• Doc/RELEASES.md — versioned changelog

MIT with Commons Clause. See Doc/LICENSE.md.