Agent Skills Spec

Agent Skills Specification Reference

SKILL.md Structure

Required Frontmatter

• name: 1-64 chars, lowercase alphanumeric + hyphens
• description: 1-1024 chars

Optional Frontmatter

• license: License identifier
• compatibility: Environment requirements (max 500 chars)
• metadata: Key-value pairs for extensibility
• allowed-tools: Space-delimited tool list

Directory Layout

skill-name/
├── SKILL.md        # Required
├── scripts/        # Executable code
├── references/     # Documentation
└── assets/         # Templates, data

Name Validation

import re

SKILL_NAME_PATTERN = re.compile(r'^[a-z][a-z0-9]*(-[a-z0-9]+)*$')

def validate_skill_name(name: str) -> bool:
    """Validate skill name against specification.

    Rules:
    - 1-64 characters
    - Lowercase letters, numbers, hyphens only
    - Must start with a letter
    - Cannot start/end with hyphen
    - No consecutive hyphens
    """
    if not 1 <= len(name) <= 64:
        return False
    if '--' in name:
        return False
    return bool(SKILL_NAME_PATTERN.match(name))

Validation Rules

• Name must match parent directory name
• No consecutive hyphens allowed
• Cannot start or end with hyphen
• Body recommended < 5000 tokens

Progressive Disclosure

1. Metadata (~100 tokens): Name and description loaded for all skills
2. Instructions (<5000 tokens): Full body loaded upon activation
3. Resources (on-demand): Scripts, references, assets loaded as needed