Use tools from any website in any MCP client.

webmcp-bridge is a CLI and Chrome extension that bridge navigator.modelContext (Chrome 146+) to MCP over stdio. The extension intercepts WebMCP tool registrations from open tabs and forwards them over a localhost WebSocket to the CLI, which exposes them as standard MCP tools.

graph LR
    A[MCP Client] -->|stdio| B[CLI] -->|websocket| C[Extension] -->|navigator.modelContext| D[Website]

Why WebMCP?

Websites already orchestrate APIs, manage auth, and handle complex workflows. A traditional MCP server rebuilds all of that from scratch. WebMCP skips it — the website registers tools client-side via navigator.modelContext, and agents call them through the browser. The tools run through the same code paths as the UI, authenticated by whatever the user already has.

| | Traditional MCP | WebMCP | | -------------- | ----------------------- | ------------------ | | Server | build and host | the website | | Auth | API keys, token refresh | browser sessions | | Business logic | reimplement | already in the UI | | Maintenance | track API changes | website handles it |

What this extension adds

WebMCP alone only talks to the browser's built-in agent. This extension bridges it to the MCP ecosystem — Claude, Cursor, Windsurf, any MCP client can call tools from any open tab.

Quick Start

npm install -g webmcp-bridge

Load the extension: chrome://extensions → Developer mode → Load unpacked → extension/

Add to your MCP client:

{
  "mcpServers": {
    "webmcp": {
      "command": "webmcp-bridge"
    }
  }
}

Open a WebMCP-enabled site. Extension badge goes green. Tools appear in your client.

Plugin Marketplace

Not every website supports WebMCP natively — the plugin marketplace lets you add tools to any site. Install community-authored bridge scripts that register MCP tools on pages that don't have them yet.

Click Manage Plugins in the extension popup to browse and install. Plugins are installed from GitHub — just enter a package specifier like user/repo and the extension handles the rest.

Want to build your own plugin? Use the /webmcp-marketplace-plugins skill in Claude Code to get started.

Development

bun install              # deps
bun test                 # unit tests
bun run test:e2e:pw      # Playwright E2E (needs Chrome Canary 146+)
bun run test:e2e:install # one-time: download Chrome for Testing Canary
bun run dev              # dev mode
bun run build            # build for npm
bun run lint             # lint
bun run chrome           # launch dev Chrome with extension
bun run chrome:dev       # launch dev Chrome + CLI together

Security

Localhost-only (127.0.0.1), random port (13100-13199), 256-bit shared secret, origin-validated, nonce-protected, 0700/0600 file perms. Details in CLAUDE.md.

License

MIT