Tip: MCP Servers Add 23k-Token Constant Context Tax — Use CLI Equivalents at Zero Cost
Simon Willison·high signal
Simon Willison's Agentic Engineering Patterns guide quantifies a critical MCP cost: the GitHub MCP server adds ~23,000 tokens of fixed overhead to every session that loads it. Models already know how to use gh, git, psql, and other common CLIs — invoking those directly costs zero context tokens. Actionable rule: use MCP servers only for tools without CLI equivalents or where structured I/O justifies the overhead.