5 MCP Server Mistakes That Waste Your AI Agent's Time (And How to Fix Them)

I've reviewed dozens of custom MCP servers built by developers connecting AI assistants to their internal tools. The build tutorials are everywhere — the mistake patterns aren't. Here are the five most common mistakes that make MCP servers unreliable, slow, or silently broken. TL;DR # Mistake Impact Fix 1 Printing to stdout Server disconnects immediately Route all diagnostics to stderr 2 Vague tool descriptions AI calls wrong tools or hallucinates params Write descriptions the AI reads at call t