Skill Builder

Skill Builder: turn a one-line brief into a review-ready skill

You are turning a brief problem statement into a finished, review-ready skill. Your job is to do the research, scope the skill to a single job, fill every layer of the template, scaffold its evals, then STOP for review. You never install, commit, or push what you scaffold.

The failure mode this skill exists to prevent is the kitchen-sink skill: a vague brief becomes a skill that tries to do three things, leads with "helps with" filler, lists every tool, and ships with half its <ANGLE_BRACKET> placeholders unfilled. Guard against it on every build — one job, trigger-first description, minimal tools, zero surviving placeholders.

When to use this skill

• "Build / create / scaffold a skill for X"
• Someone describes a recurring task — usually with a repo or an example — and wants it turned into a reusable skill
• Turning a skill brief or issue (like this repo's issues) into an actual skills/<name>/ folder

When NOT to use this skill

• Editing or reviewing an existing skill — open it and edit it directly; this skill authors new ones.
• The "skill" is really a one-off — a single shell command, a config tweak, or a permission rule. Not every task needs a skill; say so and stop. (Settings or hook changes are a config task, not a skill.)
• The brief implies several unrelated jobs — that's N skills, not one. This skill builds one at a time; propose the split (step 5).

Steps

1. Intake. Capture the brief problem, any context (repo path, an example, the specific pain point), and the target output mode. Default to portable unless a real repo is in play and the user wants the skill baked for it — then project (see Rules → Output modes).

2. Read the anatomy. Read references/skill-anatomy.md for the exact structure and quality bar you must produce. If template/ exists in the working repo, that folder is your canonical starting scaffold (cp -r template skills/<name>); otherwise reproduce the same structure from the reference.

3. Clarify — as much as it takes, no padding. Ask via AskUserQuestion until you genuinely understand the single job, its triggers, the target output mode, and the key decisions the skill must encode. A thin brief may need several rounds to become a valuable, detailed skill; a detailed brief may need none. Batch related questions (up to 4 per prompt) instead of drip-feeding, ask only what you can't settle yourself by researching the repo (step 4) or by a sensible stated default, and stop once another answer wouldn't change the scaffold — depth where it makes the skill better, never interrogation for its own sake. Never guess the skill's purpose — that is the one thing you may not invent.

4. Research. If pointed at a repo, explore it with Read / Grep / Glob — README, any existing .claude/skills/, naming and code conventions, domain vocabulary, how it runs tools — so the new skill is grounded and doesn't reinvent patterns the repo already has.

5. Scope to one job. Distill the brief to a single crisp purpose. If it implies multiple jobs, propose splitting into N named skills and confirm which to build first — then build only that one. Do not scaffold until the scope is one job.

6. Scaffold. Create the skill folder — skills/<name>/ (portable) or the target repo's .claude/skills/<name>/ (project) — and fill every placeholder: kebab name matching the folder, trigger-first description, minimal allowed-tools inferred from the job, When to use / When NOT to use, numbered Steps with explicit stop conditions, Output format, and the Rules triad.

7. Layer 3 + evals. Add a references/ file only if the skill needs a big catalog, signature table, or worked examples; otherwise omit it. Always write evals/README.md with 2–3 representative cases, including at least one negative "should not fire / should ask instead" case.

8. Self-check. Verify against the checklist in references/skill-anatomy.md: no surviving <ANGLE_BRACKET> (portable mode), name matches the folder, description leads with the trigger, allowed-tools is minimal, output is portable unless project mode was chosen. Fix anything that fails before reporting.

9. Report & stop. Print the new skill's path, a one-paragraph summary (the job and its triggers), and the evals to run. Do not install, commit, or push. Stop.

Output format

Report exactly this, then stop:

Created skill: <path>/SKILL.md   (mode: portable | project)
Job: <one sentence — the single job this skill does>
Triggers: <when Claude should fire it>
Files: SKILL.md, evals/README.md[, references/<file>]
Verify with: <the eval case names from evals/README.md>

Not done for you: not installed, not committed.
To try it: cp -r <path> ~/.claude/skills/ and run the evals in a fresh session.

Rules

What to do

• One job, always. A skill has a single purpose. If you need "and" to describe it, it is two skills — propose the split and build one.
• Trigger-first description. Lead the description with a tight statement of the job, with the trigger words a user would actually say ("build / create / scaffold a skill") right up front — it is the only layer-1 metadata and it decides whether the skill triggers at all.
• Minimal allowed-tools. List only the tools the job needs. A read-only skill lists no Write/Edit/Bash. Infer the set from the steps, not from habit; scope Bash to subcommands when you can (e.g. Bash(git status:*)).
• Ask until the job is clear — by sufficiency, not a quota. Ask as many genuine questions as it takes to scope a valuable, detailed skill; ask none if the brief already settles it. No padding, batch related ones, and never ask what you could answer by researching the repo. Ask, don't guess.
• Ship evals. Every skill gets 2–3 cases and at least one negative case — a skill without a way to prove it works is unfinished.

What NOT to do

• NEVER ship a kitchen-sink skill. Multi-job briefs get split, not crammed.
• NEVER leave a surviving <ANGLE_BRACKET> in portable output. The self-check exists to catch this.
• NEVER guess the skill's purpose. Ask, or stop — purpose is the one thing you may not invent.
• NEVER install, commit, or push the scaffold. The deliverable is files for review; landing them is the user's call.
• Don't manufacture a skill for a one-off. A single command or config change isn't a skill — say so and stop.

Output modes

• Portable (default). Placeholders, no org names, no real paths, no stack or schema assumptions — the kind of skill that ships in this repo. Everything project-specific is an <ANGLE_BRACKET> the adopter fills in.
• Project. Only when pointed at a real repo and explicitly asked: bake that repo's real paths and conventions into a skill destined for its local .claude/skills/. The skill itself stays portable — the mode governs only the output.

Format discipline

• The deliverable is the files plus a tight report. No preamble, no narrating the research, no recap. Scaffold, report, stop.

For the full structure, quality bar, and finished-skill checklist, read references/skill-anatomy.md.