Writing Agent Skills

Writing Agent Skills

Workflow: Creating a new skill

1. Clarify scope. Ask what task the skill should teach an agent to perform. Identify what context an agent lacks — that gap is the skill's content.
2. Choose a name. Lowercase, hyphens only, 1–64 chars. Prefer gerund form (e.g., processing-pdfs over pdf-processor). Must match directory name.
3. Write the description. This is the most important text in the skill — it controls when the skill activates. Write in third person. State both what the skill does AND when to use it. Include keywords matching how users phrase requests. Max 1024 chars.
4. Write the body. Use imperative form. Include only what the agent cannot already know. Keep under 500 lines (~5000 tokens).
5. Apply progressive disclosure. If content exceeds 500 lines, move detailed information into references/ files. Link from SKILL.md — keep all references one level deep (no chains).
6. Add scripts only if needed. Include bundled scripts when the same code is rewritten repeatedly or deterministic reliability matters.
7. Validate. Check against the pre-ship checklist in references/08-organizing-and-checklist.md.

Workflow: Reviewing an existing skill

1. Read the skill's SKILL.md and all bundled files.
2. Check for these common problems:
   • Weak description — vague, missing keywords, wrong point-of-view
   • Kitchen sink — body over 500 lines without progressive disclosure
   • Teaching known things — explaining what the agent already knows
   • Too many options — listing alternatives without picking a default
   • Nested references — chains deeper than one level from SKILL.md
   • Extraneous files — README.md, CHANGELOG.md, etc.
   • Inconsistent terminology — mixing synonyms for the same concept
3. Propose specific fixes with before/after examples.

Key rules

• The context window is a public good. Every token competes with conversation history. Only include what the agent cannot already know.
• Make choices for the agent. Pick a default approach; offer alternatives only for specific edge cases.
• Set appropriate degrees of freedom. Fragile operations need exact instructions; open-ended tasks need general direction.
• Description drives discovery. "When to use" belongs in the description frontmatter, not in the body.
• No extraneous files. No README, CHANGELOG, INSTALLATION_GUIDE, or QUICK_REFERENCE inside a skill.

Starter template

---
name: my-skill-name
description: "[What it does]. [What it produces or transforms]. Use when [specific triggers and contexts]."
---

# [Skill Name]

## Workflow

1. [First step]
2. [Second step]
3. [Third step]

## Examples

**Input:** [example input]
**Output:** [example output]

## Edge cases

- [Edge case 1]: [How to handle it]
- [Edge case 2]: [How to handle it]

Reference material

Consult these for detailed guidance on specific topics:

• Format & specification: references/01-overview-and-format.md
• Core principles: references/02-core-principles.md — context window economy, degrees of freedom, making choices
• Metadata & body structure: references/03-metadata-and-structure.md — name/description rules, body sections, terminology
• Progressive disclosure: references/04-progressive-disclosure.md — three-level loading, reference patterns
• Bundled resources: references/05-bundled-resources.md — scripts, references, assets guidance
• Design patterns: references/06-design-patterns.md — template, workflow, feedback loop, routing patterns
• Anti-patterns & testing: references/07-anti-patterns-and-testing.md — common mistakes, evaluation-driven development, two-instance workflow
• Organizing & checklist: references/08-organizing-and-checklist.md — scaling skills, pre-ship checklist, quick-start template