Writing Great Skills

Writing Great Skills Skill

A skill is a promise: given this kind of request, produce this kind of professional output, every time. The best SKILL.md files win on two things — the model triggers them at the right moment, and once triggered it produces the right artifact without hand-holding. This skill helps you write one that does both.

Working from a brief

Given a rough idea ("a skill for writing changelogs"), produce the full SKILL.md anyway — infer the deliverable, inputs, and structure, and mark genuinely open choices. Never hand back a skeleton with <!-- TODO --> left in; fill them.

Required Inputs

Ask for (if not already provided), else infer and label:

• What the skill should do and the concrete artifact it produces
• When it should trigger (the phrasings a user would actually type)
• The inputs it needs from the user
• Any framework or standard it encodes (for attribution)

The anatomy of a great SKILL.md

1. Frontmatter (this is what gets your skill found)

---
name: kebab-case-name           # matches the folder; short, specific
description: "<one rich sentence>"
---

The description is the most important line in the file — it's all the model sees when deciding whether to load the skill (progressive disclosure: only names + descriptions are in context until one is invoked). A strong description has three parts:

• What it does + the concrete deliverable.
• A "Use when …" trigger clause listing the real phrasings ("Use when asked to write a postmortem, do a root-cause analysis, or document an incident").
• A "Produces …" clause naming the output ("Produces a blameless postmortem with timeline, root cause, and action items").

Write triggers the way users speak, not the way you'd categorise the skill. Cover synonyms.

2. One-line value statement

Open the body with a single sentence on the value, in the voice of a senior practitioner.

3. Working from a brief

State that the skill delivers a complete artifact even with thin input — infer and label assumptions, never leave bracketed placeholders, never refuse for missing context. This is what separates a skill that works from one that nags.

4. Required Inputs

A short list of what to ask for — and an instruction to proceed with labelled inferences if they're missing.

5. Output Format / Structure

The heart of the skill: a concrete template — real headings, tables, and sections — of the final artifact. Show the shape, don't describe it abstractly. This is where most of the quality lives.

6. Quality Checks

A short checklist the output must satisfy (the rubric a reviewer would apply). Make them observable.

7. Anti-Patterns

The specific failure modes to avoid — the lazy or generic outputs a weaker model would produce.

Process

1. Nail the deliverable in one sentence before writing anything else.
2. Write the description and stress-test the triggers ("would the model pick this over a neighbouring skill?").
3. Draft the Output Format as a real template.
4. Add Quality Checks and Anti-Patterns that target this skill's specific failure modes.
5. Validate: npm run skillcheck (structure) and run it against a thin brief to confirm it doesn't beg for inputs.

Output Format

Return:

1. The complete SKILL.md in a fenced block, ready to save to skills/<name>/SKILL.md.
2. A 3–5 bullet "why this works" note: the trigger phrases chosen, the deliverable, and the sharpest anti-pattern it guards against.

Deeper Materials

This skill ships with support files — use them when they are available:

• references/description-engineering.md — Description Engineering: the 300 Characters That Decide Everything. Apply it while producing the output; it carries the calibration and judgment calls the method summary above compresses.
• templates/skill-scaffold.md — a fill-in version of the deliverable with the quality gates inline. Offer it when the user wants to work the document themselves rather than have it generated.