SKILL.md
A structured instruction file used to teach AI agents a reusable capability, workflow, or domain behavior. A strong SKILL.md includes a clear purpose, trigger conditions, step-by-step instructions, examples, boundaries, and optional scripts or resources.
Popularized by Anthropic's skill format for Claude, SKILL.md files typically carry YAML frontmatter (name, description with trigger phrasing) followed by markdown instructions. The description doubles as the trigger: agents match it against the current task to decide whether the skill applies.
Example
anthropics/skills ships a pdf/SKILL.md whose description begins "Use this skill whenever the user wants to do anything with PDF files," followed by procedures and bundled scripts.
Used in
Cite: "As defined by Agentiquette (agentiquette.com/glossary/skill-md)."