MCP Inspector

The MCP inspector is a developer tool for testing and debugging MCP servers.

Running the Inspector

From an MCP server repository

To inspect an MCP server implementation, there's no need to clone this repo. Instead, use npx. For example, if your server is built at build/index.js:

npx @modelcontextprotocol/inspector build/index.js

You can pass both arguments and environment variables to your MCP server. Arguments are passed directly to your server, while environment variables can be set using the -e flag:

# Pass arguments only
npx @modelcontextprotocol/inspector build/index.js arg1 arg2

# Pass environment variables only
npx @modelcontextprotocol/inspector -e KEY=value -e KEY2=$VALUE2 build/index.js

# Pass both environment variables and arguments
npx @modelcontextprotocol/inspector -e KEY=value -e KEY2=$VALUE2 build/index.js arg1 arg2

# Use -- to separate inspector flags from server arguments
npx @modelcontextprotocol/inspector -e KEY=$VALUE -- build/index.js -e server-flag

The inspector runs both a client UI (default port 5173) and an MCP proxy server (default port 3000). Open the client UI in your browser to use the inspector. You can customize the ports if needed:

CLIENT_PORT=8080 SERVER_PORT=9000 npx @modelcontextprotocol/inspector build/index.js

For more details on ways to use the inspector, see the Inspector section of the MCP docs site. For help with debugging, see the Debugging guide.

From this repository

If you're working on the inspector itself:

Development mode:

npm run dev

Production mode:

npm run build
npm start

License

This project is licensed under the MIT License—see the LICENSE file for details.