Claude Code Skill Development

Skill Development

Create effective Claude Code skills that are concise, discoverable, and well-structured.

Quick Reference

You MUST read these references for detailed guidance:

• Best Practices - Official Anthropic guidance
• Skill Examples - Patterns from real skills
• Skill Categories & Patterns - Three categories and five reusable patterns
• Testing Guide - Triggering, functional, and performance testing
• Troubleshooting - Common problems and fixes
• The Complete Guide to Building Skills for Claude - Comprehensive Anthropic guide (source PDF)

Before You Start

Define 2-3 concrete use cases before writing anything:

Use Case: [Name]
Trigger: User says "[phrase]" or "[phrase]"
Steps:
1. [First action]
2. [Second action]
Result: [What gets produced]

Then identify which category your skill falls into — this determines which techniques to use. See Skill Categories & Patterns.

Core Principles

1. Concise is key - Only add context Claude doesn't already have
2. Progressive disclosure - SKILL.md is the overview; details go in references/
3. Write in third person - "This skill processes..." not "I can help you..."

Skill Structure

skill-name/
├── SKILL.md              # Main instructions (< 500 lines)
├── scripts/              # Optional: executable code (Python, Bash, etc.)
├── assets/               # Optional: templates, fonts, icons
└── references/           # Detailed docs (loaded on demand)
    ├── guide.md
    └── examples/

YAML Frontmatter

---
name: my-skill-name
description: This skill should be used when the user asks to "do X", "create Y", or mentions Z. Be specific about triggers.
context: fork          # Optional: run in isolated context (prevents side effects)
user-invocable: true   # Optional: show in slash command menu (default: true)
---

Name rules:

• Lowercase letters, numbers, hyphens only
• Max 64 characters
• No reserved words (anthropic, claude)

Description rules:

• Max 1024 characters
• Third person ("This skill..." not "I can...")
• Include WHAT it does AND WHEN to use it

Optional fields:

• context: fork - Run skill in isolated sub-agent context, preventing unintended side effects on main agent state
• user-invocable: false - Hide from slash command menu (skills are visible by default)
• allowed-tools - Restrict which tools the skill can use (e.g., "Bash(python:*) Bash(npm:*) WebFetch"). Skills with references/ directories should include allowed-tools: Read, Grep to avoid permission prompts when accessing bundled files (claude-code#15757)
• license - e.g., MIT, Apache-2.0
• compatibility - Environment requirements (1-500 chars)
• metadata - Custom key-value pairs (author, version, mcp-server)

Writing Effective Descriptions

Structure: [What it does] + [When to use it] + [Key capabilities]

# Good - specific triggers
description: This skill should be used when the user asks to "create a hook", "add a hook", or mentions Claude Code hooks.

# Bad - vague
description: Helps with automation tasks.

Progressive Disclosure Pattern

Keep SKILL.md under 500 lines. Link to details:

# My Skill

## Quick start
[Essential info here]

## Advanced features
See [detailed-guide.md](./references/detailed-guide.md)

## API reference
See [api-reference.md](./references/api-reference.md)

Claude loads reference files only when needed.

Testing Your Skill

Validate across three dimensions before sharing:

1. Triggering - Does it load when it should? Not load when it shouldn't?
2. Functional - Does it produce correct outputs and handle errors?
3. Performance - Is it actually better than no skill? (fewer messages, fewer errors, less tokens)

See Testing Guide for test examples and success criteria.

Troubleshooting

Common issues and fixes:

See Troubleshooting for detailed solutions.

Important

After creating or modifying skills, inform the user:

No restart needed. Skill changes take effect immediately - skills are hot-reloaded.

Checklist

Before finalizing a skill:

• 2-3 use cases defined with triggers, steps, and results
• Category identified (document creation, workflow automation, MCP enhancement)
• Description includes triggers ("when user asks to...")
• SKILL.md under 500 lines
• Complex content moved to references/
• Third person throughout
• No time-sensitive information
• Consistent terminology
• Triggering tests pass (obvious + paraphrased requests)
• Doesn't trigger on unrelated topics