create-skill

SKILL.md

Create Skill

Guide for creating effective skills that extend agent capabilities with specialized knowledge, workflows, and tool integrations.

About Skills

Skills are modular, self-contained packages that extend agent capabilities by providing specialized knowledge, workflows, and tools. Think of them as "onboarding guides" for specific domains or tasks.

What Skills Provide

Specialized workflows - Multi-step procedures for specific domains

Tool integrations - Instructions for working with specific file formats or APIs

Domain expertise - Company-specific knowledge, schemas, business logic

Bundled resources - Scripts, references, and assets for complex and repetitive tasks

Progressive Disclosure Principle

The 200-line rule is critical. SKILL.md must be under 200 lines. If you need more, split content into references/ files.
Three-Level Loading System

Metadata (name + description) - Always in context (~100 words)

SKILL.md body - When skill triggers (<200 lines, ideally <500 lines for optimal performance)

Bundled resources - As needed by agent (unlimited)

Why Progressive Disclosure Matters

85% reduction in initial context load

Activation times drop from 500ms+ to under 100ms

Agent loads only what's needed, when it's needed

Skills remain maintainable and focused

Skill Structure

skill-name/
├── SKILL.md (required, <200 lines)
│   ├── YAML frontmatter metadata (required)
│   │   ├── name: (required)
│   │   └── description: (required)
│   └── Markdown instructions (required)
└── Bundled Resources (optional)
    ├── scripts/          - Executable code
    ├── references/       - Documentation loaded as needed
    └── assets/           - Files used in output

Core Principles

Concise is Key

The context window is a shared resource. Your skill shares it with everything else the agent needs. Be concise and challenge each piece of information:

Does the agent really need this explanation?

Can I assume the agent knows this?

Does this paragraph justify its token cost?

Set Appropriate Degrees of Freedom

High freedom: Text-based instructions for multiple valid approaches

Medium freedom: Pseudocode or scripts with parameters

Low freedom: Specific scripts with few/no parameters for fragile operations

Test with All Models

Skills act as additions to models, so effectiveness depends on the underlying model. Test your skill with all models you plan to use it with.

References

For detailed guidance, see:

references/progressive-disclosure.md - 200-line rule and references pattern

references/skill-structure.md - SKILL.md format and frontmatter details

references/examples.md - Good skill examples

references/best-practices.md - Comprehensive best practices guide