Every MCP server you connect sends its full tool list to the model before the model does anything. You pay for that list on every single turn, whether the agent uses one of those tools or none of them. I had a rough sense this was expensive.
Source: [Dev.to](https://dev.to/onlyoneaman/the-median-mcp-server-costs-3150-tokens-before-your-agent-calls-anything-4np3)