Claude Code skills answer a specific pain: you keep pasting the same checklist into chat, or a section of your CLAUDE.md has quietly grown from facts about the project into a multi-step procedure. The official guidance is exactly that — when instructions become a procedure you re-explain, move them into a skill. Unlike CLAUDE.md content, a skill's body loads only when it's used, so a long runbook costs you almost nothing until the moment you need it.
This post covers the SKILL.md format end to end: the frontmatter fields, how triggering actually works, arguments, supporting files, and a template you can copy.
The mental model: two-stage loading
Everything about writing a good skill follows from one design fact:
The description is always visible. Claude sees your skill's name and description in every session, and uses them to decide when the skill is relevant.
