MCP Workbench

A visual debugger and test client for Model Context Protocol (MCP) servers.

MCP Workbench lets you connect to an MCP server over Streamable HTTP, inspect protocol traffic, explore resources, and execute tools with zero guesswork. It’s built for developers who want fast feedback and full visibility into what their server is actually doing.

What This Tool Is For

• Debugging MCP servers during development
• Verifying protocol compliance (handshake, capabilities, message flow)
• Manually testing tools, prompts, and resources
• Inspecting raw JSON-RPC traffic in real time

If you’re building or maintaining an MCP server, this is your control panel.

Features

• Streamable HTTP Client**

• Session handling via MCP-Session-Id

• Auto-generated input forms from JSON Schema

• Execute tools and inspect raw responses

• Browse and inspect server-exposed resources

• List and test available prompts

• Authentication Support

  • OAuth 2.0 (Authorization Code flow with popup)
  • API key support via custom headers

• Multi-Server Configs

  • Save, switch, and reuse multiple MCP server connections

Getting Started

Requirements

• Node.js 18+
• npm or yarn

Setup

git clone https://github.com/conductoross/mcp-workbench.git
cd mcp-workbench
npm install
npm run dev

Open:

http://localhost:5173

Testing Local Stdio Servers (Node.js/Python)

To connect the Workbench to a local MCP server running over Stdio (e.g. node server.js), use the included Bridge script:

1. Run the bridge with your command:

   node scripts/stdio-bridge.js "node my-server.js"
   # or for Python
   node scripts/stdio-bridge.js "uv run main.py"
   

2. Copy the URL printed (e.g., http://localhost:3001/mcp)

3. In Workbench, select Streamable HTTP and paste the URL.

CORS Handling

Your MCP server must allow cross-origin requests from the Workbench origin. If CORS is misconfigured, requests will fail silently in the browser.

Safari requires an additional CORS header for localhost:

Access-Control-Allow-Private-Network: true

Add this to your server's CORS middleware. Chrome and Firefox are more permissive.

Contributing

Pull requests are welcome. Keep changes focused, readable, and aligned with MCP specifications.

License

MIT License