zen-mcp

zen-mcp

The first MCP server for Zen Browser. Automate Zen from Claude Code, Cursor, or any MCP client.

No Selenium. No Playwright. No browser drivers. Just WebSocket.

Setup (2 minutes)

1. Start Zen with remote debugging

/Applications/Zen.app/Contents/MacOS/zen --remote-debugging-port 9222

Pro tip: Add alias zen='open /Applications/Zen.app --args --remote-debugging-port 9222' to your shell config. Then just run zen.

2. Add to Claude Code

# Option A: npm (recommended)
npm install -g zen-mcp

# Option B: Clone
git clone https://github.com/sh6drack/zen-mcp.git && cd zen-mcp && npm install

Add to ~/.claude/mcp_servers.json:

{
  "mcpServers": {
    "zen-browser": {
      "command": "zen-mcp"
    }
  }
}

If you cloned instead of npm install, use "command": "node", "args": ["/absolute/path/to/zen-mcp/server.mjs"]

Add to ~/.claude/settings.json:

{
  "permissions": {
    "allow": ["mcp__zen-browser__*"]
  }
}

That's it. Start a new Claude Code session and the zen_* tools are available.

20 Tools

Browse

| Tool | What it does | |------|-------------| | zen_navigate | Go to a URL | | zen_list_pages | List all open tabs | | zen_select_page | Switch to a tab | | zen_new_tab | Open a new tab | | zen_close_tab | Close a tab |

See

| Tool | What it does | |------|-------------| | zen_snapshot | Page structure with selectors (filter: all/interactive/form) | | zen_screenshot | Capture a screenshot | | zen_get_page_text | Get page title, URL, and text | | zen_get_form_fields | List all form fields with labels and values |

Interact

| Tool | What it does | |------|-------------| | zen_click | Click an element | | zen_fill | Type into an input or textarea | | zen_select_option | Pick a dropdown option | | zen_check | Toggle a checkbox or radio | | zen_press_key | Keyboard input (Enter, Tab, Ctrl+A, etc.) | | zen_fill_form | Fill multiple fields at once | | zen_scroll | Scroll the page or to an element |

Utility

| Tool | What it does | |------|-------------| | zen_evaluate | Run JavaScript in the page | | zen_wait | Wait N milliseconds | | zen_wait_for | Wait for text or element to appear | | zen_reconnect | Force reconnect to Zen |

How It Works

Claude Code  ──stdio/MCP──>  zen-mcp  ──WebSocket/BiDi──>  Zen Browser

zen-mcp speaks WebDriver BiDi (W3C standard) directly over WebSocket. Form filling uses native value setters with input/change event dispatch so React, Vue, and Angular apps work correctly.

What Works Well

• Navigation, clicking, form filling — rock solid, handles React/Vue/Angular
• Screenshots and page reads — reliable content extraction
• Tab management — open, close, switch between tabs
• JavaScript evaluation — run any code in the page context
• Keyboard input — shortcuts, Enter, Tab, modifier combos

Known Limitations

• Zen inherits Firefox's WebDriver BiDi implementation, which is still maturing. Some advanced BiDi commands that work in Chrome may not be available yet.
• Zombie sessions can only be cleared by restarting Zen (BiDi session.end is connection-scoped). zen-mcp detects this and tells you what to do.
• No file upload or drag-and-drop support (BiDi spec limitation).

Built-in Reliability

• Auto-reconnect with exponential backoff if WebSocket drops
• Zombie session recovery when a previous client crashed
• Connection retry (3 attempts with backoff)
• Clean shutdown on SIGINT/SIGTERM to prevent orphaned sessions

Troubleshooting

| Problem | Fix | |---------|-----| | "Cannot connect to Zen Browser" | Start Zen with --remote-debugging-port 9222 | | "Maximum number of active sessions" | Restart Zen: killall zen && zen | | Connection keeps dropping | Use zen_reconnect to force a fresh connection |

Config

| Env Variable | Default | Description | |-------------|---------|-------------| | ZEN_DEBUG_PORT | 9222 | Zen's remote debugging port |

Requirements

• Zen Browser
• Node.js 20+

Test

node test-e2e.mjs   # 21 tests, needs Zen running

License

MIT