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