/create-skill

name: create-skill
description: Guide for creating effective skills. This command should be used when users want to create a new skill (or update an existing skill) that extends Claude's capabilities with specialized knowledge, workflows, or tool integrations. Use when creating new skills, editing existing skills, or verifying skills work before deployment - applies TDD to process documentation by testing with subagents before writing, iterating until bulletproof against rationalization

Create Skill Command

This command provides guidance for creating effective skills.

Overview

**Writing skills IS Test-Driven Development applied to process documentation.**

**Personal skills live in agent-specific directories (`~/.claude/skills` for Claude Code, `~/.codex/skills` for Codex)**

You write test cases (pressure scenarios with subagents), watch them fail (baseline behavior), write the skill (documentation), watch tests pass (agents comply), and refactor (close loopholes).

**Core principle:** If you didn't watch an agent fail without the skill, you don't know if the skill teaches the right thing.

**REQUIRED BACKGROUND:** You MUST understand Test-Driven Development before using this skill. That skill defines the fundamental RED-GREEN-REFACTOR cycle. This skill adapts TDD to documentation.

**Official guidance:** The Anthropic's official skill authoring best practices provided at the `/apply-anthropic-skill-best-practices` command, they enhance `prompt-engineering` skill. Use skill and the document, as they not copy but add to each other. These document provides additional patterns and guidelines that complement the TDD-focused approach in this skill.

About Skills

Skills are modular, self-contained packages that extend Claude's capabilities by providing specialized knowledge, workflows, and tools. Think of them as "onboarding guides" for specific domains or tasks—they transform Claude from a general-purpose agent into a specialized agent equipped with procedural knowledge that no model can fully possess.

What is a Skill?

A **skill** is a reference guide for proven techniques, patterns, or tools. Skills help future Claude instances find and apply effective approaches.

**Skills are:** Reusable techniques, patterns, tools, reference guides

**Skills are NOT:** Narratives about how you solved a problem once

What Skills Provide

1. Specialized workflows - Multi-step procedures for specific domains 2. Tool integrations - Instructions for working with specific file formats or APIs 3. Domain expertise - Company-specific knowledge, schemas, business logic 4. Bundled resources - Scripts, references, and assets for complex and repetitive tasks

TDD Mapping for Skills

| TDD Concept | Skill Creation | |-------------|----------------| | **Test case** | Pressure scenario with subagent | | **Production code** | Skill document (SKILL.md) | | **Test fails (RED)** | Agent violates rule without skill (baseline) | | **Test passes (GREEN)** | Agent complies with skill present | | **Refactor** | Close loopholes while maintaining compliance | | **Write test first** | Run baseline scenario BEFORE writing skill | | **Watch it fail** | Document exact rationalizations agent uses | | **Minimal code** | Write skill addressing those specific violations | | **Watch it pass** | Verify agent now complies | | **Refactor cycle** | Find new rationalizations → plug → re-verify |

The entire skill creation process follows RED-GREEN-REFACTOR.

When to Create a Skill

**Create when:**

• Technique wasn't intuitively obvious to you
• You'd reference this again across projects
• Pattern applies broadly (not project-specific)
• Others would benefit

**Don't create for:**

• One-off solutions
• Standard practices well-documented elsewhere
• Project-specific conventions (put in CLAUDE.md)

Skill Types

Technique

Concrete method with steps to follow (condition-based-waiting, root-cause-tracing)

Pattern

Way of thinking about problems (flatten-with-flags, test-invariants)

Reference

API docs, syntax guides, tool documentation (office docs)

Directory Structure

skills/
  skill-name/
    SKILL.md              # Main reference (required)
    supporting-file.*     # Only if needed

**Flat namespace** - all skills in one searchable namespace

**Separate files for:**

1. **Heavy reference** (100+ lines) - API docs, comprehensive syntax 2. **Reusable tools** - Scripts, utilities, templates

**Keep inline:**

• Principles and concepts
• Code patterns (< 50 lines)
• Everything else

Anatomy of a Skill

Every skill consists of a required SKILL.md file and optional bundled resources:

skill-name/
├── SKILL.md (required)
│   ├── YAML frontmatter metadata (required)
│   │   ├── name: (required)
│   │   └── description: (required)
│   └── Markdown instructions (required)
└── Bundled Resources (optional)
    ├── scripts/          - Executable code (Python/Bash/etc.)
    ├── references/       - Documentation intended to be loaded into context as needed
    └── assets/           - Files used in output (templates, icons, fonts, etc.)

SKILL.md (required)

**Metadata Quality:** The `name` and `description` in YAML frontmatter determine when Claude will use the skill. Be specific about what the skill does and when to use it. Use the third-person (e.g. "This skill should be used when..." instead of "Use this skill when...").

SKILL.md Structure

**Frontmatter (YAML):**

• Only two fields supported: `name` and `description`
• Max 1024 characters total
• `name`: Use letters, numbers, and hyphens only (no parentheses, special chars)
• `description`: Third-person, includes BOTH what it does AND when to use it
• Start with "Use when..." to focus on triggering conditions
• Include specific symptoms, situations, and contexts
• Keep under 500 characters if possible

---
name: Skill-Name-With-Hyphens
description: Use when [specific triggering conditions and symptom