Agent Skills Validator

A PHP library for validating Agent Skills SKILL.md files according to the agentskills.io specification.

Based on validator.py

Installation

Install via Composer:

composer require ronaldtebrake/agent-skills-validator

Requirements

• PHP 8.1 or higher
• Symfony Filesystem component (^6.0 || ^7.0)

Usage

use AgentSkills\Validator\Validator;

$validator = new Validator();
$result = $validator->validateSkill('/path/to/skill/directory');

if ($result['valid']) {
    echo "Skill is valid!\n";
    print_r($result['metadata']);
} else {
    echo "Validation errors:\n";
    foreach ($result['errors'] as $error) {
        echo "  - $error\n";
    }
}

Return Format

The validateSkill() method returns an array with the following structure:

[
    'valid' => bool,        // Whether the skill passed validation
    'errors' => string[],   // Array of error messages (empty if valid)
    'metadata' => array     // Parsed frontmatter metadata
]

Validation Rules

The validator enforces the following rules per the Agent Skills specification:

Required Fields

• name: Must be a non-empty string, lowercase, max 64 characters, containing only letters, digits, and hyphens. Cannot start/end with hyphens or contain consecutive hyphens. Must match the directory name.
• description: Must be a non-empty string, max 1024 characters.

Optional Fields

• license: Any string value
• allowed-tools: Array of tool names
• metadata: Object with arbitrary key-value pairs
• compatibility: String, max 500 characters

File Structure

• The skill directory must contain a SKILL.md file
• The file must have valid YAML frontmatter delimited by ---
• Only the allowed fields listed above may be present in the frontmatter

Example SKILL.md

---
name: my-awesome-skill
description: A skill that does something awesome
license: MIT
compatibility: Requires PHP 8.1+
metadata:
  author: John Doe
  version: "1.0.0"
---
# My Awesome Skill

This skill provides awesome functionality for AI agents.

CLI Tool for CI/CD

The package includes a CLI tool for validating skills in CI/CD environments. When installed via Composer, the binary is available at vendor/bin/agent-skills-validator:

# Validate all skills in a directory (automatically discovers subdirectories with SKILL.md)
vendor/bin/agent-skills-validator .claude/skills

# When running from the repository directly
php bin/agent-skills-validator .claude/skills

# If no path is provided, it defaults to the current directory
vendor/bin/agent-skills-validator

Directory Discovery: If you provide a directory path that doesn't contain a SKILL.md file, the tool will automatically search for all subdirectories containing SKILL.md files and validate them. If a directory already contains SKILL.md, it will be validated directly.

The CLI tool exits with code 0 on success and 1 if validation fails, making it suitable for CI/CD pipelines.

GitHub Actions Example

Create .github/workflows/validate-skills.yml:

name: Validate Agent Skills

on:
  pull_request:
    paths:
      - '**/SKILL.md'
      - '**/*/SKILL.md'

jobs:
  validate:
    runs-on: ubuntu-latest
    
    steps:
      - uses: actions/checkout@v3
      
      - name: Setup PHP
        uses: shivammathur/setup-php@v2
        with:
          php-version: '8.1'
      
      - name: Install dependencies
        run: composer install --no-interaction --prefer-dist
      
      - name: Validate skills
        run: vendor/bin/agent-skills-validator .claude/skills

Testing

Run the test suite:

composer install
vendor/bin/phpunit

Specification Reference

This validator implements the validation rules from the Agent Skills specification, based on the reference implementation at agentskills/agentskills.

License

MIT License - see LICENSE file for details.