Skill Creator

Guide for creating effective skills that extend Claude's capabilities.

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—they transform Claude from a general-purpose agent into a specialized agent equipped with procedural knowledge.

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 tasks

Core Principles

Concise is Key

The context window is a public good. Skills share context with system prompts, conversation history, other skills, and user requests.

Default assumption: Claude is already very smart. Only add context Claude doesn't already have. Challenge each piece: "Does Claude really need this?" and "Does this justify its token cost?"

Prefer concise examples over verbose explanations.

Set Appropriate Degrees of Freedom

Match specificity to task fragility:

Think of Claude exploring a path: narrow bridge needs guardrails (low freedom), open field allows many routes (high freedom).

Grey Haven Skill Anatomy

Every Grey Haven skill follows this structure:

skill-name/
├── SKILL.md (required)
│   ├── YAML frontmatter (required)
│   │   ├── name: grey-haven-{skill-name}
│   │   ├── description: (comprehensive, includes triggers)
│   │   ├── skills: (optional, v2.0.43)
│   │   └── allowed-tools: (optional, v2.0.74)
│   └── Markdown body (required)
└── Bundled Resources (optional)
    ├── scripts/      - Executable code
    ├── references/   - Documentation for context
    ├── examples/     - Usage examples
    ├── templates/    - Reusable templates
    └── checklists/   - Validation checklists

SKILL.md Frontmatter

---
name: grey-haven-your-skill
description: "What the skill does. When to use it. Trigger phrases."
# v2.0.43: Auto-load these skills when this skill activates
skills:
  - grey-haven-code-style
  - grey-haven-testing-strategy
# v2.0.74: Restrict available tools when skill is active
allowed-tools:
  - Read
  - Write
  - Bash
  - TodoWrite
---

Description is critical: This is the primary trigger mechanism. Include:

• What the skill does
• When to use it
• Specific trigger phrases

Bundled Resources

Progressive Disclosure

Skills use a three-level loading system:

1. Metadata (~100 words) - Always in context
2. SKILL.md body (<5K words) - When skill triggers
3. Bundled resources - As needed by Claude

Keep SKILL.md under 500 lines. Split into reference files when approaching this limit. Always reference split files from SKILL.md with clear "when to read" guidance.

Skill Creation Process

Step 1: Understand with Concrete Examples

Before creating, understand concrete usage:

• "What functionality should this skill support?"
• "Give examples of how this skill would be used."
• "What would a user say that should trigger this skill?"

Conclude when you clearly understand the functionality needed.

Step 2: Plan Reusable Contents

Analyze each example:

1. How would you execute this from scratch?
2. What scripts, references, assets would help when doing this repeatedly?

Example analyses:

Step 3: Initialize the Skill

Run the initialization script:

python scripts/init_skill.py my-skill --path grey-haven-plugins/core/skills

This creates:

• SKILL.md template with TODO placeholders
• Example resource directories
• Proper structure for Grey Haven

Step 4: Edit the Skill

Writing Guidelines:

• Use imperative/infinitive form
• Challenge every paragraph's token cost
• Prefer examples over explanations

Frontmatter:

• name: Use grey-haven- prefix
• description: Include what + when + triggers
• skills: Optional dependent skills
• allowed-tools: Optional tool restrictions

Body:

• Start with clear overview
• Include practical examples
• Reference bundled resources with "when to read" guidance

Design Patterns (see references/):

• Multi-step processes: See references/workflows.md
• Output formats: See references/output-patterns.md

Step 5: Test and Iterate

After creating:

1. Use the skill on real tasks
2. Notice struggles or inefficiencies
3. Update SKILL.md or resources
4. Test again

What NOT to Include

Skills should only contain essential files. Do NOT create:

• README.md (SKILL.md is the readme)
• INSTALLATION_GUIDE.md
• CHANGELOG.md
• User-facing documentation
• Process documentation

The skill is for Claude, not humans. Include only what helps Claude do the job.

Grey Haven Conventions

Naming

• Skill name: grey-haven-{domain}-{function}
• Directory: skills/{skill-name}/
• Examples: grey-haven-tdd-python, grey-haven-api-design-standards

Description Format

description: "{What it does}. {When to use it}. Triggers: '{trigger1}', '{trigger2}', '{trigger3}'."

File Organization

skill-name/
├── SKILL.md
├── examples/
│   └── practical-example.md
├── references/
│   └── detailed-guide.md
├── templates/
│   └── reusable-template.md
└── checklists/
    └── validation-checklist.md

Quick Start

# Initialize new skill
python scripts/init_skill.py my-new-skill --path grey-haven-plugins/core/skills

# Edit the generated SKILL.md
# Add resources as needed
# Test with real usage

Skill Version: 1.0 Based on: Anthropic skill-creator (Dec 2025) Last Updated: 2025-01-15