What is inside an AI agent skill?

A skill is a reusable, packaged capability that an AI agent loads when it needs it. In practice it is a folder built around a single instructions file (SKILL.md), with optional scripts, reference material, and assets alongside.^[1] Where a prompt is something you type, a skill is something the agent keeps and reaches for.

The instructions file has a small piece of front matter, usually a name and a description, followed by the body that tells the agent how to do the task. That front matter is doing more work than it looks like: it is the only part of the skill loaded by default, so it has to be specific enough that the agent recognizes the right moment to reach for the rest — see progressive disclosure for why that matters. Around the instructions body, a skill can bundle:

• Scripts the agent can run directly, instead of writing the same code from scratch every time the task comes up.
• References it can read for detail too long to keep in the main instructions — a full API spec, a style guide, an edge-case list.
• Assets like templates, example files, or boilerplate the task starts from rather than generates.

None of these are required. The simplest skill is a SKILL.md file and nothing else. The folder structure exists so a skill can grow past a few paragraphs without becoming unreadable, not because every skill needs all three. This structure is also what makes a skill portable: it travels as a folder, not as a paragraph buried in a chat, which is why it can be checked into a repository, reviewed like any other code, and reused by anyone who has it — see an open standard for how far that portability actually reaches.