Don't Build Your MCP Server as an API Wrapper

The Model Context Protocol (MCP) is gaining traction as the standard way to connect language models to external systems. And the first instinct of most engineers who already have a REST API is entirely predictable: wrap it. One tool per endpoint, one parameter per query string, done in an afternoon. It compiles, it runs, the model can technically call it - and it will perform badly in production. Here is why that instinct is wrong, and what to do instead.