Mud: Mark Up or Down

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 need 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 every 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.

Gimme

Download Mud.app:

• macOS App Store
• GitHub

Highlights

The Feature Showcase demonstrates Mud's markdown rendering!

• 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 (default), Riot
• Auto / Bright / Dark 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

Command line tool

Install from Mud > Install Command Line Tool… 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

License

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