106 MCP servers measured: tool-schema context cost spans 1,700x, GitHub's official server eats 27% of a 200K window
aksh_stocks · reddit · 2026-09-05
The author measured the tools/list context tokens injected by 106 popular MCP servers (83 have numbers), with a fully reproducible method: raw-wire stdio client in credential-free Docker, captures published with SHA-256 and launch commands.
Key findings:
- 1,700x spread: postgres costs 32 tokens; GitHub's official server costs 54,622 — 27% of a 200K context window before the agent does anything.
- Cost is uncorrelated with popularity: chrome-devtools (3.3M weekly installs) costs 5,717 tokens across 29 tools, while comfyui-mcp (4% of that install base) costs 50,640.
- The badge number isn't the Claude number: Anthropic requests carry only name/description/inputschema with a different tokenizer; notion goes from 17,500 to 33,560 on claude-opus-5, with ratios spanning 0.20x–1.92x — no constant multiplier exists.
- Claude Code's deferred loading is nearly free, but server instructions bytes go uncounted; deepwiki's instructions exceed its tool definitions.
- An independent Rust implementation (mcp-tokens) agrees within 1%; 17 of 83 servers moved over time (11 up, 6 down), obsidian +82% in a week.
npx -y mcp-context-cost audit audits your Claude Desktop/Code, Cursor, VS Code and Windsurf configs; --baseline/--max-increase turn it into a CI gate, plus shields badges and a five-line GitHub Action for publishers.
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