mo

mo is a Markdown viewer that opens .md files in a browser.

Features

• GitHub-flavored Markdown (tables, task lists, footnotes, etc.)
• Syntax highlighting (Shiki)
• Mermaid diagram rendering
• Dark / light theme
• File grouping
• Table of contents panel
• Flat / tree sidebar view with drag-and-drop reorder
• Live-reload on save

Install

homebrew tap:

$ brew install k1LoW/tap/mo

manually:

Download binary from releases page

Usage

$ mo README.md                          # Open a single file
$ mo README.md CHANGELOG.md docs/*.md   # Open multiple files
$ mo spec.md --target design            # Open in a named group

mo opens Markdown files in a browser with live-reload. When you save a file, the browser automatically reflects the changes.

Single server, multiple files

By default, mo runs a single server on port 6275. If a server is already running on the same port, subsequent mo invocations add files to the existing session instead of starting a new one.

$ mo README.md          # Starts a mo server in the background
$ mo CHANGELOG.md       # Adds the file to the running mo server

To run a completely separate session, use a different port:

$ mo draft.md -p 6276

Groups

Files can be organized into named groups using the --target (-t) flag. Each group gets its own URL path and sidebar.

$ mo spec.md --target design      # Opens at http://localhost:6275/design
$ mo api.md --target design       # Adds to the "design" group
$ mo notes.md --target notes      # Opens at http://localhost:6275/notes

Sidebar view modes

The sidebar supports flat and tree view modes. Flat view shows file names only, while tree view displays the directory hierarchy.

Flat	Tree

Starting and stopping

mo runs in the background by default — the command returns immediately, leaving the shell free for other work. This makes it easy to incorporate into scripts, tool chains, or LLM-driven workflows.

$ mo README.md
mo: serving at http://localhost:6275 (pid 12345)
$ # shell is available immediately

Use --status to check all running mo servers, and --shutdown to stop one:

$ mo --status              # Show all running mo servers
$ mo --shutdown            # Shut down the mo server on the default port
$ mo --shutdown -p 6276    # Shut down the mo server on a specific port

If you need the mo server to run in the foreground (e.g. for debugging), use --foreground:

$ mo --foreground README.md

Server restart

Click the restart button (bottom-right corner) to restart the mo server process. The current session — all open files and groups — is preserved across the restart. This is useful when you have updated the mo binary and want to pick up the new version without re-opening your files.

Flags

Flag	Short	Default	Description
--target	-t	default	Group name
--port	-p	6275	Server port
--open			Always open browser
--no-open			Never open browser
--status			Show all running mo servers
--shutdown			Shut down the running mo server
--foreground			Run mo server in foreground

Build

Requires Go and pnpm.

$ make build

References

• yusukebe/gh-markdown-preview: GitHub CLI extension to preview Markdown looks like GitHub.