Creating Skills

Creating Skills

Guide for creating Claude Code skills following Anthropic's official best practices.

Quick Start

# 1. Create skill directory
mkdir -p ~/.claude/skills/<skill-name>/references

# 2. Create SKILL.md with frontmatter
cat > ~/.claude/skills/<skill-name>/SKILL.md << 'EOF'
---
name: <skill-name>
description: <what it does>. Use when <trigger phrases>. <key capabilities>.
---

# <Skill Title>

<One-line description>

## Quick Start
<Minimal steps to use the skill>

## Core Workflow
<Step-by-step instructions>

## Important Rules
<Critical constraints and requirements>
EOF

# 3. Add helper scripts if value-add
# 4. Add reference files for detailed docs

SKILL.md Structure

Frontmatter (REQUIRED)

---
name: skill-name          # lowercase, hyphens, no spaces
description: <desc>       # CRITICAL for discovery (max 1024 chars)
---

Frontmatter (OPTIONAL - New in v2.1.0)

---
name: skill-name
description: <desc>
context: fork             # Run in forked context (protects main context)
agent: general-purpose    # Execute as specific agent type
---

Description Formula

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

Example:

Creates GitHub Pull Requests with automated validation. Use when user wants
to create PR, open pull request, or merge feature. Validates tasks, runs
tests, generates Conventional Commits format.

Trigger phrases to include:

• Action verbs: "create", "handle", "manage", "process"
• User intent: "wants to", "needs to", "asks for"
• Keywords users would say: "PR", "pull request", "review comments"

Body Sections (ORDER MATTERS)

1. Title - # Skill Name
2. One-liner - Single sentence summary
3. Quick Start - Minimal steps (copy-paste ready)
4. Core Workflow - Numbered steps with code blocks
5. Helper Scripts (if any) - Table with purpose
6. Important Rules - Critical constraints (bold ALWAYS/NEVER)

Naming Conventions

Format Options

Rules

• Lowercase only
• Hyphens between words (no underscores)
• No spaces
• Descriptive but concise (2-4 words)

Token Budget

If approaching 500 lines:

1. Move detailed examples to references/examples.md
2. Move troubleshooting to references/troubleshooting.md
3. Keep SKILL.md focused on workflow

Helper Scripts Guidelines

When to Create Scripts

DO create scripts for:

• Complex logic (severity classification, commit analysis)
• Multi-step processing with JSON output
• Reusable utilities across invocations

DON'T create scripts for:

• Single command wrappers (gh api ...)
• Simple operations Claude can do inline
• One-line bash commands

Script Requirements

#!/usr/bin/env python3
"""Script description."""

import json
import sys

def main():
    # Read from stdin or args
    # Process data
    # Output JSON to stdout
    print(json.dumps(result))

if __name__ == "__main__":
    main()

• Output JSON for structured data
• Use stdin/stdout for piping
• Include clear error messages
• Keep focused on single responsibility

Directory Structure

~/.claude/skills/<skill-name>/
├── SKILL.md              # Main skill file (< 500 lines)
├── scripts/              # Optional helper scripts
│   └── helper.py         # Only if value-add
└── references/           # Optional detailed docs
    ├── examples.md       # Extended examples
    └── guide.md          # Deep-dive documentation

Core Principles

1. Claude is Already Smart

"Default assumption: Claude is already very smart. Only add context Claude doesn't already have."

Challenge each line:

• Does Claude really need this explanation?
• Can I assume Claude knows this?
• Does this paragraph justify its token cost?

2. Progressive Disclosure

SKILL.md (primary)
    ↓ references/ (when needed)
        ↓ external links (rarely)

• Start minimal, expand as needed
• Don't front-load all information
• Let Claude discover details when relevant

3. User Confirmation for Critical Actions

**ALWAYS** confirm before:
- Modifying files
- Running destructive commands
- Creating external resources (PRs, issues)

4. Structured Output

Prefer JSON for script output:

# Good: Structured, parseable
python3 script.py | jq '.result'

# Bad: Unstructured text
python3 script.py | grep "Result:"

Quality Checklist

Before finalizing a skill:

• Frontmatter: name + description present
• Description: includes WHAT + WHEN triggers + capabilities
• Naming: lowercase, hyphens, descriptive
• Quick Start: copy-paste ready, < 30 lines
• Line count: SKILL.md < 500 lines
• Scripts: only value-add, no wrappers
• Rules: critical constraints marked with bold
• Test: skill triggers on expected phrases
• Context protection: Use context: fork for large content processing
• Bash permissions: Use wildcard patterns (Bash(git *)) instead of verbose

Bash Wildcard Permission Patterns (v2.1.0)

For commands that use allowed-tools, use wildcard patterns for cleaner permissions:

# Old (verbose)
allowed-tools:
  - Bash(git -C:*)
  - Bash(git config:*)
  - Bash(git log:*)
  - Bash(git show:*)

# New (concise with wildcards)
allowed-tools:
  - Bash(git *)      # All git commands
  - Bash(npm *)      # All npm commands
  - Bash(mkdir *)    # mkdir with any args
  - Bash(pwd)        # Exact match (no args)

Pattern Types:

Anti-Patterns to Avoid

Important Rules

• ALWAYS include frontmatter with name and description
• ALWAYS include trigger phrases in description
• ALWAYS keep SKILL.md under 500 lines
• ALWAYS use lowercase-hyphen naming
• NEVER create wrapper scripts for simple commands
• NEVER over-explain things Claude already knows
• NEVER include multiple competing workflows