MCP Inspector

Debugging an MCP server usually starts here: the Model Context Protocol project maintains Inspector as the official test harness, runnable with a single npx @modelcontextprotocol/inspector command on Node.js 22.19 or later. One global binary exposes three interfaces: a web UI built on Vite, React, and Mantine for interactive exploration, a scriptable CLI for automation and CI assertions, and an Ink-based terminal TUI for staying in the shell. Each can connect to servers over stdio, SSE, or streamable HTTP, then list and invoke tools, read resources, exercise prompts, and watch raw protocol traffic, which makes malformed schemas and broken capability negotiation visible immediately. The MIT-licensed repository sits at about 10,700 stars, with active development on the v2 line while v1 receives security fixes only. Because it ships from the same organization that maintains the protocol specification, Inspector doubles as a reference for correct MCP behavior, and most server tutorials assume it is the first thing anyone runs against a new build.