The invisible bill I was debugging why my Claude Code sessions felt sluggish after connecting a few MCP servers. Token usage was through the roof -- but I hadn't even asked the agent to do anything yet. I rewrote my prompts three times before I thought to check where the tokens were actually going. Turns out, the moment you connect an MCP server, every tool definition gets loaded into the context window. Names, descriptions, parameter schemas, enum values -- all of it, on every single conversation turn. Not just when you call a tool. Every turn. Think of it like walking into a library to read one book, but the librarian insists you read the entire catalog first. Every time you walk in. The measurement: 4 servers, 500x cost difference I measured the tool-definition token overhead for four MCP servers, from minimal to massive: MCP Server Tools Est.…