Every MCP server you connect ships a set of tool-definition schemas. Those schemas get injected into every single model request for the whole session — before you ask the agent anything. That's a fixed tax on your context window and your bill, and no MCP directory lists it.
So I measured it. I pulled 25 popular Model Context Protocol servers, spawned each one locally, ran the real tools/list handshake, and counted the tokens its tool schemas add per request (chars/4, the same heuristic tokenscope uses — labelled an estimate). 16 of the 25 register their tools without live credentials, so those are measured; the rest need OAuth/remote transport or real keys and are marked not measured, never estimated.
The context-tax, measured
Server
Tools
