MCP Inspector

MCP Inspector is the official, open-source developer tool for testing and debugging Model Context Protocol servers. It's the fastest way to see what a server actually exposes: connect to it, browse its tools, resources, and prompts, call them with arbitrary inputs, and watch the raw request/response traffic — all from a local web UI, with no client and no model in the loop.

It is aimed at anyone building an MCP server who wants to confirm a capability behaves before wiring it into Claude Code or another client. Because it talks to your server directly, it separates "is my server correct?" from "is the model using it well?" — so you debug one problem at a time.

Highlights

• Connect to any MCP server — launch a local stdio server as a child process, or point it at a remote Streamable HTTP server by URL.
• Exercise every primitive — list and call tools with custom arguments, read resources, and render prompts, seeing typed inputs and results.
• See the wire — inspect the JSON-RPC messages, notifications, and errors flowing in both directions, which is where most server bugs reveal themselves.
• Zero install — run it on demand with npx; it opens a browser UI against your server.

In an AI-assisted workflow

Point the Inspector at the server you're developing and click through its tools before any client touches it:

# launch the Inspector against a local stdio server
npx @modelcontextprotocol/inspector node ./my-server/index.js

It opens a UI where you connect, list the server's tools, call one with sample inputs, and read back the result and any errors — the tight loop that catches a bad schema or a vague description early.

Good to know

MCP Inspector is free and open source under MIT and maintained as part of the Model Context Protocol project. You run it locally via Node.js (npx @modelcontextprotocol/inspector), and it's the standard first stop when building a server with a framework like FastMCP or the official SDKs.