po

po 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
• LaTeX math rendering (KaTeX)
• GitHub Alerts (admonitions)
• Fullscreen zoom modal for images and Mermaid diagrams
• Dark / light theme
• File grouping
• Table of contents panel
• Flat / tree sidebar view with drag-and-drop reorder
• File name / heading title sidebar display toggle (per-group)
• Full-text search across file names and content
• Codex app-server backed agentic repository search with --repo --agentic-search
• YAML frontmatter display (collapsible metadata block)
• MDX file support (renders as Markdown, strips import/export, escapes JSX tags)
• Content font size toggle (small / medium / large / extra large)
• Wide / narrow content width toggle
• Raw markdown view
• Copy content (Markdown / Text / HTML)
• Server restart with session preservation
• Auto session backup and restore
• Drag-and-drop file addition from the OS file manager (content is loaded in-memory; live-reload is not supported for dropped files)
• Stdin pipe support (cat file.md | po)
• Live-reload on save (for files opened via CLI)

Install

homebrew tap:

$ brew install k1LoW/tap/po

manually:

Download binary from releases page

Usage

$ po README.md                          # Open a single file
$ po README.md CHANGELOG.md docs/*.md   # Open multiple files
$ po docs/                              # Open all .md files in a directory
$ po spec.md --target design            # Open in a named group
$ po --repo                             # Open all repo Markdown files
$ po --repo README.md                   # Use /repo-name?file=relative/path URLs
$ po --repo --agentic-search            # Enable Codex-backed search
$ cat notes.md | po                     # Read Markdown from stdin

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

Reading from stdin

When no positional arguments are given and stdin is redirected (not a terminal), po reads Markdown content from stdin.

$ cat notes.md | po
$ some-command | po --target output
$ po < notes.md

The content is loaded in-memory with a generated name (stdin-<hash>.md). Piping the same content again reuses the existing entry (deduplicated by content hash).

Single server, multiple files

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

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

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

$ po draft.md -p 6276

Repository-scoped URLs

Use --repo when you want links to be scoped to the current Git repository instead of exposing file URLs as machine-local entries. po detects the repository root, uses the repository name as the URL path, and addresses files by path relative to that root.

With no file arguments, po --repo opens all Markdown files in the repository. It respects .gitignore by default, including tracked files and untracked files that are not ignored. Use --no-ignore to include ignored Markdown files too.

$ po --repo
# http://localhost:6275/po

$ po --repo README.md
# http://localhost:6275/po?file=README.md

$ po --repo docs/guide.md
# http://localhost:6275/po?file=docs/guide.md

$ po --repo --no-ignore

Pass a path to use a specific repository:

$ po --repo=/path/to/repo /path/to/repo/docs/guide.md

Add --agentic-search with --repo to enable the search panel's Codex button. The server starts codex app-server for each request, runs it with a read-only sandbox from the repository root, and returns the answer to the browser. Enable it only for repositories that are appropriate to inspect with Codex.

Groups

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

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

Watch mode and glob patterns

--watch (-w) turns on watch mode. Directory and glob positional arguments are registered as watch patterns, matching files are opened, and new matching files are picked up automatically.

$ po -w '**/*.md'                              # Watch and open all .md files recursively
$ po -w 'docs/**/*.md' --target docs           # Watch docs/ tree in "docs" group
$ po -w '*.md' 'docs/**/*.md'                  # Multiple patterns (positional)
$ po -w docs/                                  # Watch docs/*.md

Combine with --recursive (-R) to descend into subdirectories. Short flags can be combined:

$ po -w -R docs/                               # Watch docs/**/*.md
$ po -wR docs/                                 # Same, short-combined

Without --watch, globs are expanded once and directory arguments open matching files without live-watching new additions:

$ po docs/                                     # Open every .md directly in docs/
$ po -R docs/                                  # Open every .md under docs/ (recursive)
$ po 'docs/*.md'                               # Expand and open matching .md files

Removing watch patterns

--unwatch removes previously registered patterns. Pass glob patterns or directories as positional arguments to specify which patterns to remove. Regular file paths are not accepted (use --close to remove individual files from the sidebar). Files already added by a pattern remain in the sidebar.

$ po --unwatch '**/*.md'                              # Stop watching a pattern (default group)
$ po --unwatch docs/                                  # Stop watching docs/*.md
$ po --unwatch 'docs/**/*.md' --target docs            # Stop watching in a specific group

With -R, a directory argument removes all registered patterns under that directory at once. For example, if docs/*.md, docs/sub/*.md, and docs/**/*.md are all registered, a single command removes them all:

$ po --unwatch -R docs/                               # Removes docs/*.md, docs/sub/*.md, docs/**/*.md, etc.

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

Sidebar view modes

The sidebar uses tree view by default and can be switched to flat view. Tree view displays the directory hierarchy, while flat view shows file names only and supports drag-and-drop reorder.

Flat	Tree

Starting and stopping

po 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.

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

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

$ po --status              # Show all running po 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

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

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

$ po --foreground README.md

Server restart

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

Session backup and restore

po 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.

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

Use --close to remove specific files from the running server:

$ po --close README.md            # Close a file from the default group
$ po --close docs/*.md -t docs    # Close files from the "docs" group

Use --clear to remove a saved session. If a server is running, it is automatically restarted with an empty state:

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

JSON output

Use --json to get structured JSON output on stdout, useful for scripting and integration with other tools.

$ po --json README.md
{
  "url": "http://localhost:6275",
  "files": [
    {
      "url": "http://localhost:6275/?file=a1b2c3d4",
      "name": "README.md",
      "path": "/Users/you/project/README.md"
    }
  ]
}

--status also supports --json:

$ po --status --json
[
  {
    "url": "http://localhost:6275",
    "status": "running",
    "pid": 12345,
    "version": "0.15.0",
    "revision": "abc1234",
    "groups": [
      {
        "name": "default",
        "files": 3,
        "patterns": ["**/*.md"]
      }
    ]
  }
]

Flags

Flag	Short	Default	Description
--target	-t	default	Group name
--port	-p	6275	Server port
--bind	-b	localhost	Bind address (e.g. 0.0.0.0)
--open			Always open browser
--no-open			Never open browser
--status			Show all running po servers
--watch	-w	false	Treat directory and glob arguments as watch patterns
--unwatch		false	Remove watched patterns for the given directory or glob arguments
--recursive	-R	false	Recurse into subdirectories when a directory is given
--close			Close files instead of opening them
--shutdown			Shut down the running po server
--restart			Restart the running po server
--clear			Clear saved session (restarts server if running)
--foreground			Run po server in foreground
--json			Output structured data as JSON to stdout
--repo			Use Git repository-scoped URLs; optional value is a path inside the repo
--no-ignore		false	Include ignored Markdown files when opening all files with --repo
--agentic-search		false	Enable Codex app-server backed repository search (requires --repo)
--dangerously-allow-remote-access			Allow remote access without authentication (trusted networks only)

Warning

Binding to a non-localhost address exposes po to the network without any authentication. Remote clients can read any file accessible by the user, browse the filesystem via glob patterns, and shut down the server. If --agentic-search is enabled, remote clients can also start read-only Codex app-server searches against the repository. A confirmation prompt is shown when --bind is set to a non-loopback address.

Build

Requires Go and pnpm.

$ make build

References

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

License

• MIT License
  • Include logo as well as source code.
  • Only logo license can be selected CC BY 4.0.
  • Also, if there is no alteration to the logo and it is used for technical information about po, I would not say anything if the copyright notice is omitted.