# MCP (Model Context Protocol)

Band: established — Settled. Documented by a primary source and not seriously disputed.
Group: The harness

An open standard for connecting AI applications to external systems — data, tools, prompts — implemented by Claude, ChatGPT, VS Code, Cursor and many others, so a server built once integrates everywhere. Adoption is its strongest argument. The cost vendor material omits is real: most clients load every tool definition up front, so descriptions occupy the window before any work starts, and every intermediate result round-trips through the model. Install servers casually and you pay that tax on every single turn.

## See also

- [Hook](https://clickai.dev/legend/hook)
- [Prompt injection](https://clickai.dev/legend/prompt-injection)
- [Prompt caching](https://clickai.dev/legend/prompt-caching)

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Full legend: https://clickai.dev/legend.md