Most teams install an MCP server and hope it works. That is how you get 3 AM pages. An MCP server is a bridge between AI agents and your tools. It can crash, leak data, or silently return garbage. If your AI agent relies on it, your whole pipeline breaks. MCP means Model Context Protocol (standard tool link). Do not only test startup. Test behavior and permissions too. This post is the checklist I run on every MCP server before it touches production. The three-layer test stack Layer What it catches Tool Discovery Missing tools, broken metadata MCP Inspector Behavior Silent failures, wrong output pytest smoke tests Security Over-permissions, data leaks Permission audit Layer 1: Discovery with MCP Inspector MCP Inspector is the official debugging tool. Start it with: npx @anthropic-ai/mcp-inspector node dist/server.js Enter fullscreen mode Exit fullscreen mode Check three things: Does the server start without errors? Does it list the tools it promises? Does a sample request return the right shape?…