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-gassed 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.