Metro MCP Server

metro-mcp

A plugin-based MCP server for React Native runtime debugging, inspection, and automation. Connects to Metro bundler via Chrome DevTools Protocol — no app code changes needed for most features.

Works with Expo, bare React Native, and any project using Metro + Hermes.

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Contents

• Quick Start
• Requirements
• How It Works
• Features
• Chrome DevTools
• Claude Code Status Bar
• Test Recording
• App Integration
• Configuration
• Custom Plugins
• Compatibility

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Quick Start

Claude Code

claude mcp add metro-mcp -- npx -y metro-mcp
# or with Bun
claude mcp add metro-mcp -- bunx metro-mcp

Codex

codex mcp add metro-mcp -- npx -y metro-mcp
# or with Bun
codex mcp add metro-mcp -- bunx metro-mcp

Codex stores MCP servers in ~/.codex/config.toml by default, and the Codex CLI and IDE extension share that configuration.

If you prefer to configure it manually:

[mcp_servers.metro-mcp]
command = "npx"
args = ["-y", "metro-mcp"]

Cursor / VS Code

{
  "mcpServers": {
    "metro-mcp": {
      "command": "npx",
      "args": ["-y", "metro-mcp"]
    }
  }
}

Or with Bun:

{
  "mcpServers": {
    "metro-mcp": {
      "command": "bunx",
      "args": ["metro-mcp"]
    }
  }
}

With custom Metro port

codex mcp add metro-mcp -- npx -y metro-mcp --port 19000
# or
claude mcp add metro-mcp -- npx -y metro-mcp --port 19000

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Requirements

• Node.js 18+ or Bun 1.0+
• iOS: Xcode 14+ with Simulator (xcrun simctl is used for most operations)
• Android: Android SDK with adb on your PATH
• IDB (optional): Some iOS operations fall back to IDB (idb-companion) — install with brew install idb-companion. Tools will tell you when IDB is needed.

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How It Works

metro-mcp connects to your running Metro dev server the same way Chrome DevTools does:

1. Discovers Metro via port scanning (8081, 8082, 19000–19002)
2. Connects to Hermes via Chrome DevTools Protocol (CDP)
3. Streams console logs, network requests, and errors into buffers
4. Exposes everything as MCP tools, resources, and prompts

No app modifications required for core debugging features.

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Features

→ See the full tools reference.

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Chrome DevTools

Hermes (the React Native JavaScript engine) only allows a single CDP debugger connection at a time. Since metro-mcp uses that connection, pressing "j" in Metro or tapping "Open Debugger" in the dev menu will steal the connection and disconnect the MCP.

metro-mcp solves this with a built-in CDP proxy that multiplexes the single Hermes connection, allowing Chrome DevTools and the MCP to work simultaneously.

Opening DevTools

Use the open_devtools MCP tool instead of the usual methods. It opens the same React Native DevTools frontend (rn_fusebox) that Metro uses, but routes the WebSocket connection through the proxy so both can coexist.

The tool automatically finds Chrome or Edge using the same detection as Metro and opens a standalone DevTools window.

What to avoid

Configuration

The CDP proxy is enabled by default. To change the port or disable it:

# Set a fixed proxy port
METRO_MCP_PROXY_PORT=9222 npx metro-mcp

# Disable the proxy entirely
METRO_MCP_PROXY_ENABLED=false npx metro-mcp

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Claude Code Status Bar

Get live Metro CDP connection status in your Claude Code status bar.

Run setup_statusline in Claude Code — it writes a script to ~/.claude/metro-mcp-statusline.sh, then ask Claude to add it to your status bar:

/statusline add the script at ~/.claude/metro-mcp-statusline.sh

The status bar segment shows three states:

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Test Recording

Record real user interactions (taps, text entry, scrolls) and generate production-ready tests — no app code changes required.

AI-driven test generation

Describe a flow and the AI navigates the app, then generates the test:

"Write an Appium test for the guest checkout flow — start by tapping 'Start Shopping' on the welcome screen and end when the cart screen is visible."

The AI calls start_test_recording, navigates using tap_element/type_text/swipe, then generates a complete test with real selectors observed from the fiber tree.

Manual recording

start_test_recording   → inject interceptors
(interact with the app)
stop_test_recording    → retrieve event log
generate_test_from_recording format=appium

Supports Appium (WebdriverIO), Maestro YAML, and Detox.

→ See the testing guide for full details, format examples, and tips.

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App Integration (Optional)

Register custom commands and expose state to the MCP server — no package needed. Add this to your app entry point in dev mode:

if (__DEV__) {
  globalThis.__METRO_BRIDGE__ = {
    commands: {
      // Run custom actions from the MCP client
      login: async ({ email, password }) => {
        return await authService.login(email, password);
      },
      resetOnboarding: () => {
        AsyncStorage.removeItem('onboarding_completed');
      },
      switchUser: ({ userId }) => {
        store.dispatch(switchUser(userId));
      },
    },
    state: {
      // Expose state snapshots readable via get_redux_state
      userStore: () => useUserStore.getState(),
    },
  };
}

Use list_commands and run_command to call these from the MCP client.

For enhanced features like real-time Redux action tracking, navigation events, performance marks, and React render profiling, install metro-bridge — see the client SDK docs and profiling guide.

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Configuration

See configuration docs for environment variables, CLI arguments, and config file options.

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Custom Plugins

metro-mcp is fully extensible. See the plugins guide to build your own tools and resources.

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Compatibility

• React Native: 0.70+ (Hermes required)
• Expo: SDK 49+
• Runtime: Node.js 18+ or Bun 1.0+
• Platforms: iOS Simulator, Android Emulator, physical devices via USB

License

MIT