Skill Creator

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Adapted from skill-creator implementations by Anthropic and OpenAI:
https://github.com/anthropics/skills/tree/main/skills/skill-creator
https://github.com/openai/skills/tree/main/skills/.system/skill-creator

References:
- Agent Skills specification: https://agentskills.io/specification
- Skill authoring best practices: https://platform.claude.com/docs/en/agents-and-tools/agent-skills/best-practices
- Validation library: https://github.com/agentskills/agentskills/tree/main/skills-ref
-->

Create a New Skill

Guide the user through creating a new agent skill following the Agent Skills specification. Follow each step in order.

Step 1: Understand the Skill

Gather requirements before writing anything.

Ask the user:

1. What should this skill do? (one sentence)
2. When should an agent use it? (trigger phrases users would say)
3. What tools does the skill need? (Read, Grep, Glob, Bash, Task, WebFetch, etc.)
4. Where should the skill live? (which plugin or directory)

Determine the skill name:

• Lowercase letters, digits, and hyphens only (a-z, 0-9, -)
• 1-64 characters; must not start or end with -; no consecutive hyphens (--)
• Descriptive and unique among existing skills
• Prefer action-oriented names: processing-pdfs, fix-issue, code-review
• Check the target skills directory to avoid name collisions

Choose a complexity tier:

Read ${CLAUDE_SKILL_ROOT}/references/design-principles.md for guidance on keeping skills focused and concise.

Step 2: Plan the Skill

Analyze how each use case would be executed from scratch. Identify what reusable resources would help when executing these tasks repeatedly.

For each concrete example, ask:

1. What code would be rewritten every time? → candidate for scripts/
2. What documentation is needed to inform decisions? → candidate for references/
3. What templates or assets are used in output? → candidate for assets/

Example analysis:

• "Rotate a PDF" → rotating requires rewriting the same code → scripts/rotate_pdf.py
• "Query BigQuery metrics" → need table schemas each time → references/schema.md
• "Build a frontend app" → same boilerplate HTML/React → assets/hello-world/

Step 3: Study Existing Skills

Before writing, study 1-2 existing skills that match the chosen tier. Look for skills in the target repository or plugin to understand local conventions.

Read ${CLAUDE_SKILL_ROOT}/references/skill-patterns.md for concrete examples of each tier.

Also read CLAUDE.md (or AGENTS.md) at the repository root for repo-specific conventions that the skill should follow.

Step 4: Write the SKILL.md

Create <skill-directory>/<name>/SKILL.md.

Frontmatter

The YAML frontmatter must be the first thing in the file. No comments or blank lines before ---.

---
name: <skill-name>
description: <what it does>. Use when <trigger phrases>. <key capabilities>.
---

Required fields:

• name — must match the directory name exactly
• description — up to 1024 chars, no angle brackets (< or >); include trigger keywords that help agents match user intent

Optional fields:

• allowed-tools — comma-separated list (e.g., Read, Grep, Glob, Bash); omit to allow all tools
• license — license name or path (add when vendoring external content)
• metadata — arbitrary key-value mapping for additional metadata
• compatibility — environment requirements (max 500 chars); most skills don't need this

For Claude Code-specific fields (argument-hint, disable-model-invocation, context, etc.), read ${CLAUDE_SKILL_ROOT}/references/claude-code-extensions.md.

Description Guidelines

The description is the primary trigger mechanism — it determines when agents activate the skill. All "when to use" information belongs here, not in the body.

Write in third person:

• Good: "Processes Excel files and generates reports. Use when..."
• Bad: "I can help you process Excel files" or "You can use this to..."

Include natural trigger phrases:

# Good — specific triggers users would actually say
description: Security code review for vulnerabilities. Use when asked to "security review", "find vulnerabilities", "check for security issues", "audit security".

# Bad — too vague, no trigger phrases
description: A helpful skill for code quality.

Pattern: <What it does>. Use when <trigger phrases>. <Key capabilities>.

Body Guidelines

Write the body in imperative voice — these are instructions, not documentation.

Structure:

1. Start with a one-line summary of what the skill does
2. Organize steps with ## Step N: Title headings
3. Use tables for decision logic and mappings
4. Include concrete examples of expected output
5. End with validation criteria or exit conditions

For workflow and output patterns, read:

• ${CLAUDE_SKILL_ROOT}/references/workflow-patterns.md — sequential workflows, feedback loops, plan-validate-execute
• ${CLAUDE_SKILL_ROOT}/references/output-patterns.md — template, examples, and structured data patterns

Size limits:

• Keep SKILL.md under 500 lines (< 5000 tokens recommended)
• If approaching the limit, move reference material to references/ files
• Load reference files conditionally based on context (not all at once)

Use consistent terminology — pick one term for each concept and stick with it throughout. Don't alternate between "API endpoint", "URL", "route", and "path".

Attribution

If the skill is based on or adapted from external sources, add an HTML comment after the frontmatter closing ---:

---
name: example
description: ...
---

<!--
Based on [Original Name] by [Author/Org]:
https://github.com/example/original-source
-->

Step 5: Create Supporting Files

What to Include

Only include files that directly support the skill's function.