Skill

A teachable capability bundled as a unit — instructions and resources for doing one task well, kept in the environment and loaded into the context window only when relevant. The unit of progressive disclosure in a harness.

Avoid: "tool" — a tool is what the agent calls; a skill is instructions it reads.

Usage:

"Where should I put the deploy runbook?"

"As a skill — the agent loads it only when the task involves deploys. In AGENTS.md it'd burn tokens on every turn for something we use weekly."