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

• 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 and file search
• YAML frontmatter display (collapsible metadata block)
• MDX file support (renders as Markdown, strips import/export, escapes JSX tags)
• Raw markdown view
• Copy content (Markdown / Text / HTML)
• Server restart with session preservation
• Auto session backup and restore
• Live-reload on save

homebrew tap:

$ brew install k1LoW/tap/mo

manually:

Download binary from releases page

$ 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.

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

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

Use --watch (-w) to specify glob patterns. Matching files are opened automatically, and watched directories are monitored for new files.

$ mo --watch '**/*.md'                          # Watch and open all .md files recursively
$ mo --watch 'docs/**/*.md' --target docs       # Watch docs/ tree in "docs" group
$ mo --watch '*.md' --watch 'docs/**/*.md'      # Multiple patterns

--watch cannot be combined with file arguments. The ** pattern matches directories recursively.

Use --unwatch to stop watching a previously registered pattern. Files already added remain in the sidebar.

$ mo --unwatch '**/*.md'                              # Stop watching a pattern (default group)
$ mo --unwatch 'docs/**/*.md' --target docs            # Stop watching in a specific group
$ mo --unwatch '/Users/you/project/**/*.md'            # Stop watching by absolute path

Patterns are resolved to absolute paths before matching, so you can specify either a relative glob or the full path shown by --status.

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

Flat	Tree

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
http://localhost:6275 (pid 12345, v0.12.0)
  default: 5 file(s)
    watching: /Users/you/project/src/**/*.md, /Users/you/project/*.md
  docs: 2 file(s)
    watching: /Users/you/project/docs/**/*.md

$ mo --shutdown            # Shut down the mo server on the default port
$ mo --shutdown -p 6276    # Shut down the mo server on a specific port
$ mo --restart             # Restart the mo server on the default port

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

$ mo --foreground README.md

Click the restart button (bottom-right corner) or run mo --restart 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.

mo automatically saves session state (open files and watch patterns per group) when files are added or removed. When starting a new server, the previous session is automatically restored and merged with any files specified on the command line. Restored session entries appear first, followed by newly specified files.

$ mo README.md CHANGELOG.md       # Start with two files
$ mo --shutdown                   # Shut down the server
$ mo                              # Restores README.md and CHANGELOG.md
$ mo TODO.md                      # Restores previous session + adds TODO.md

Use --clear to remove a saved session:

$ mo --clear                      # Clear saved session for the default port
$ mo --clear -p 6276              # Clear saved session for a specific port

Requires Go and pnpm.

$ make build

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