Mud: A Perfect Markdown Viewer

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.

Mud requires macOS Sonoma (14.0) or higher, and comes in two flavors:

• GitHub Releases — includes Git change waypoints, CLI, Open In Browser, and Sparkle auto-updates.
• Mac App Store — sandboxed for complete safety, updates through the App Store.

• GitHub-flavored Markdown with syntax-highlighted code blocks
• Full support for macOS Quick Look and thumbnail previews in Finder
• Comments! Take notes for yourself and your collaborators, or chat with your agent
• Change tracking! See what your coding agent is doing to the document
• Reload automatically every time the file is saved to disk
• Table of contents — document outliner in sidebar
• Four color themes — Austere, Blues, Earthy, Riot
• Dark mode, Bright mode, or let your system decide
• Find (Cmd+F)
• Print and Open In Browser
• Zoom, readable column, word wrap, and line number toggles
• Mermaid diagrams, drawn in your theme’s colors
• High-quality presentation of math equations
• Native popovers for footnotes
• Collapsible YAML frontmatter
• GFM Alerts and Status blockquote styles
• Foldable headings — collapse the sections you aren’t reading
• Open a folder to get a tree of every Markdown document inside it
• Excellent command-line tools (Direct release, mostly)
• Configure Mud to open the document in your editor with a click or a keystroke

The Feature Showcase demonstrates Mud’s Markdown rendering.

I wrote an overview of my current Claude Code workflow, and how Mud is a great fit for it:

• Plan-based workflows with Claude Code & Mud

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.