Skills package instructions, and optionally scripts and resources, into a unit Claude can invoke. Custom slash commands have converged into this model. Build a Skill for a real procedure in your repo and make it robust enough for someone else to use.
What to build
- Pick a genuinely repeated procedure — releasing, adding an endpoint, writing a migration.
- Create the skill directory with a SKILL.md carrying name and description frontmatter.
- Write the description so it states when to use the skill, not just what it is — that text is the selection signal.
- Add any supporting scripts or reference files the procedure needs.
- Invoke it on a fresh task and note where the instructions were ambiguous.
- Tighten it, then have someone else run it without explanation.
Done when
- The skill runs end to end without you narrating missing steps.
- The description would let a model pick this skill over a similar one.
- It lives in version control and is reviewable like code.
- You can explain how a skill differs from a CLAUDE.md instruction in when it loads.
If you want to go further
- Explore running the skill in its own context so its intermediate work does not fill the main window.
The trap this exercise teaches
Writing a description that names the skill rather than its trigger. Selection quality is bounded by description quality — the same rule as tool descriptions.
Before you start
The theory behind this build is covered in Skills and custom slash commands. If any step below is unfamiliar, read that first — the exercise assumes it. Primary source: Claude Code Docs — Skills.
Check yourself against the exam
This exercise sits in Domain 2, which is 20% of the CCAR‑F exam. Once you have built it, run a domain drill in the study app and see whether the questions read differently.