Skills

You already have a container for procedures you invoke: the prompt file, run when you type a slash command. Some repeated knowledge does not fit that shape. Take a team convention like the audit-event rule in this course’s scenario: every significant event is recorded through the shared library’s audit helper, same call shape, same fields, same naming, in every repo. It is not always-on context you want hanging over every request, and it is not quite a task you choose to run - it is a procedure that applies whenever the work touches an audited event, including moments you did not think to flag.

You want something the agent reaches for on its own. That is a skill.

What a skill is - and isn’t

Two containers you have already met - and a third this chapter adds - make the distinctions the point of the chapter:

• A rule is always-on. Loaded into every request as background context - your conventions, your stack, your house style. You never invoke it; it is just there. (Rules chapter)
• A prompt file is invoked by you. You type its slash command and it runs; otherwise it sits inert. (Prompt files chapter)
• A skill is a self-contained, model-invoked procedure. It sits on disk with a description of when it applies, and Copilot pulls it in on its own when a task matches that description. You do not trigger it; the agent recognizes the moment and loads the steps.

The audit-event convention is a clean candidate. It is not wanted on every request, and you do not want the burden of remembering to invoke it - you want the agent to recognize “this task records an audit event” and apply the team’s recorded procedure automatically, in every repo that carries the skill, every time. Skills are also where VS Code’s prompt files documentation points (as of October 2026): prompt files run only in the Local harness, so reusable procedures for other harnesses go into skills.

What this chapter does

You will package the audit-event convention as a portable SKILL.md, get the one-line trigger right so Copilot actually reaches for it, and then see the payoff that reaches past Copilot entirely:

• Create · SKILL.md - the folder, the file, the two required frontmatter fields, where skills live, and what else a skill can carry.
• Trigger · the description does the work - why that one description line decides whether the skill ever fires.
• The standard · the cross-tool skill - the shared Agent Skills format, and what it means that your other agents may read the same file.

Start by writing the file. Create a skill.