Skill

A skill is a packaged procedure an agent can pick up when a task calls for it. In practice it is a folder with a SKILL.md describing what the skill does and when to use it, followed by the step-by-step instructions, and sometimes scripts or templates alongside. The harness shows the agent only the name and description until the skill is invoked, then loads the body into context. That makes skills a working example of progressive disclosure.

Skills exist because repeated instructions rot in chat. A deploy procedure you explain in a prompt is gone when the session ends, and the version you paste next week drifts from the version you pasted last week. Putting it in a skill gives it a home, a name, and a single place to fix. The failure mode is the same as with AGENTS.md: skills that try to do too much, or ten near-duplicate skills whose descriptions blur together so the agent picks the wrong one.

Write a skill for anything you have explained twice. Keep the description specific enough that the agent can tell when it applies. Put deterministic steps in scripts the skill can run, and keep the prose for judgment calls. Skills differ from a slash command, which you trigger by hand, in that the agent can choose to use a skill itself, and from a subagent in that a skill runs inside the current session's context rather than in a separate one.