inspector

The MCP Inspector is a developer tool that combines an interactive web UI (MCPI) with an MCP Proxy (MCPP) to test and debug MCP servers. MCPI provides a React-based frontend you can use in your browser to connect to MCP servers via the proxy, supporting multiple transport methods such as stdio, SSE, and streamable HTTP. The proxy acts as both an MCP client (to your MCP server) and an HTTP server (to serve the UI), enabling browser-based interaction with servers that use different transports. You typically start the inspector with a single command (via npx) and then open the MCPI UI in your browser on port 6274, with the MCPP proxy listening on port 6277 by default. You can customize ports if needed (e.g., CLIENT_PORT and SERVER_PORT) and you can point the inspector to run a server directly by passing the server’s startup command and any desired environment variables.

When inspecting a server, you can run the inspector in UI mode by invoking the npx command, or you can inspect a server implementation directly by passing node build/index.js (or your server’s start command) to the inspector. The UI offers server-entry and full “Servers File” export options, so you can copy a single server configuration or export a complete mcp.json payload for use in clients such as Cursor, Claude Code, or the Inspector CLI. The inspector also supports authentication through a proxy session token for SSE connections, and you can manage tokens via the UI or via URL parameters. The documentation also warns about security considerations: the proxy may spawn local processes and should not be exposed to untrusted networks.

Prerequisites:

• Node.js v22.x (as recommended by the project)
• npm (comes with Node.js) or pnpm/yarn if you prefer

Installation steps:

1. Ensure Node.js is installed. You can verify with: node --version npm --version

2. Install and run the MCP Inspector using npx (no global install required): npx @modelcontextprotocol/inspector

3. Access the UI in your browser at http://localhost:6274. The default MCPP proxy runs on port 6277 unless overridden.

4. Optional: Run a server directly via the inspector by passing your server command and environment variables, for example: npx @modelcontextprotocol/inspector node build/index.js

5. If you prefer to use Docker, you can run the inspector container as described in the README. See the Docker example in the repository for exact commands.

• The MCP Inspector uses two main components: the MCPI UI (web UI) and the MCPP proxy. The proxy connects to your MCP server using stdio, SSE, or streamable-http transports and serves the UI.
• Authentication for the proxy is supported via a session token. When enabled, the token is shown in the proxy console and can be pre-filled in the UI URL. You can disable authentication with the DANGEROUSLY_OMIT_AUTH environment variable, but this is highly discouraged due to security risks.
• Ports are 6274 for the MCPI client UI and 6277 for the MCPP proxy by default. You can customize them by setting CLIENT_PORT and SERVER_PORT when starting the inspector, e.g. CLIENT_PORT=8080 SERVER_PORT=9000 npx @modelcontextprotocol/inspector node build/index.js.
• The Servers File export feature helps you generate mcp.json configurations for reuse in other tools and clients. A single server entry or a full mcp.json file can be exported and imported into clients like Cursor, Claude Code, or the Inspector CLI.
• The inspector’s proxy is intended for local use with MCP servers; exposing it to untrusted networks can pose security risks because it can spawn local processes and connect to any configured MCP server.