skill-writing-guide

Skill Writing Guide

Overview

Use this guide to create Agent Skills that are easy to discover, quick to load, and reliable in repeated use. A skill should teach an agent how to perform a task, not record how one person solved it once.

When To Use

Use this skill when:

• Creating a new skills/<name>/SKILL.md.
• Reviewing a pull request that adds or changes a skill.
• Turning repeated agent behavior into reusable instructions.
• Deciding whether content belongs in a skill, a script, or regular documentation.

Do not use it for one-off project notes, private runbooks, or generic documentation that agents can already infer from standard tools.

Workflow

1. Define the trigger.

Write the frontmatter description as a Use when... sentence that describes the situation where the skill should load.

1. Keep the skill operational.

Prefer short instructions, decision points, verification steps, and concrete examples. Avoid essays and background stories.

1. Separate heavy material.

Keep SKILL.md focused. Move long API references, generated examples, or reusable scripts into supporting files beside the skill.

1. Add one strong example.

Use a realistic example that demonstrates the workflow end-to-end. Do not add several shallow examples.

1. Add verification.

Explain how the agent should prove the skill was used correctly before claiming completion.

1. Run repository validation.

Run python3 scripts/validate-skills.py before opening a pull request.

Skill Checklist

• Folder name uses lowercase kebab-case.
• SKILL.md starts with YAML frontmatter.
• Frontmatter includes name and description.
• Frontmatter name matches the folder name.
• Description starts with Use when.
• Body explains workflow and verification.
• Public examples contain no secrets or private data.

Verification

Before publishing a new or updated skill:

• Run python3 scripts/validate-skills.py and confirm zero errors.
• Confirm the frontmatter name matches the folder name exactly.
• Confirm the description starts with Use when and describes the trigger situation.
• Confirm at least one realistic example and one verification section exist in the body.
• Confirm no secrets, internal URLs, or private tool assumptions are in the public skill.

Common Failures

• Description summarizes the workflow: descriptions are for discovery; the body is for process.
• Skill is too broad: split unrelated workflows into separate skills.
• No verification: the agent cannot know whether the workflow succeeded.
• Too much copied reference material: link to public docs or move concise references into supporting files.
• Private assumptions: public skills should not depend on private tools unless the trigger says so.

Example

Bad description:

description: Explains how to gather context, write a document, run checks, and open a PR

Better description:

description: Use when drafting release notes from repository commits and pull requests

The better version tells the agent when to load the skill without tempting it to skip the actual instructions.