What MCP tools cost
Every tool in an MCP server sends its complete JSON schema -- name, description, parameter definitions, return types -- with every request. Ten tools might add 2,000 tokens. Fifty tools add 10,000 or more. Unlike conversation history, tool schemas are not summarized or truncated. They are sent in full, every time.
The scaling problem
As AI agents become more capable, they need access to more tools. A customer support agent might start with 5 tools and grow to 50. Each tool added increases the per-call cost linearly. This is the opposite of the efficiency curve teams expect when scaling AI systems.
At GPT-4o pricing ($2.50 per million input tokens), 50 tools at 200 tokens each costs $0.025 per call. At 10,000 calls per day, that is $7,500 per month in tool schema tokens alone. And this cost grows every time a new tool is added.