What Is SKILL.md? A Complete Guide to AI Agent Skills

If you've been using AI coding agents like Claude Code, OpenClaw, Codex CLI, or Cursor, you've probably seen people talking about "skills" — packaged instructions that make your agent better at specific tasks. At the heart of this ecosystem is a simple file called SKILL.md. This guide covers everything you need to know: what SKILL.md is, how the format works, how AI agents discover and use skills, and how to get started installing or creating your own. What is SKILL.md? SKILL.md is a markdown file that teaches an AI coding agent how to perform a specific task. Think of it like a detailed playbook: it tells the agent what to do, when to do it, and how to do it well. Each skill is self-contained in a folder. At minimum, that folder contains one file — SKILL.md — with two parts: YAML frontmatter at the top (between --- markers) that holds metadata like the skill's name, description, and configuration options Markdown instructions below the frontmatter that the agent follows when the skill