skill-validator

A PHP library to parse and validate SKILL.md files or raw SKILL.md content against the SKILL.md format specification.

Installation and usage

composer require stolt/skill-validator

Usage

The SkillMd class from the stolt/skill-md package is the primary abstraction for a validated skill: every valid result exposes a SkillMd instance, and the validator also accepts SkillMd instances directly as input.

The validator can validate existing SKILL.md files, raw SKILL.md content, or SkillMd instances.

Validating a SKILL.md file

use Stolt\Ai\Skill\Validator;

$validator = new Validator();
$result = $validator->validateFile('/path/to/an-ai-skill/SKILL.md');

Validating all SKILL.md files in a directory

use Stolt\Ai\Skill\Validator;

$validator = new Validator();
$results = $validator->validateFromDirectory('/path/to/skills');

foreach ($results as $filePath => $result) {
    if ($result->isInvalid()) {
        echo sprintf('Invalid: %s', $filePath) . PHP_EOL;
        foreach ($result->errors() as $error) {
            echo '  - ' . $error . PHP_EOL;
        }
    }
}

The method returns an array<string, ValidationResult> keyed by absolute file path, covering all SKILL.md files found recursively under the given directory.

Validating raw SKILL.md content

use Stolt\Ai\Skill\Validator;

$validator = new Validator();
$result = $validator->validateContent('raw-skill-content');

Validating a SkillMd instance

use Stolt\Ai\Skill\Validator;
use Stolt\Ai\SkillMd;

$skillMd = SkillMd::create(
    'code-review',
    'Review code changes and provide actionable feedback.',
    "# Code review\n\nReview the changed files and report issues.",
    ['tags' => ['php', 'review'], 'version' => '1.0.0']
);

$validator = new Validator();
$result = $validator->validateSkillMd($skillMd);

Tip

The validate alias method accepts a file path, directory path, raw content, or a SkillMd instance and delegates to the appropriate method automatically.

Accessing validation results and metadata

Validation returns a Stolt\Ai\Skill\ValidationResult object. When the SKILL.md content is valid, a SkillMd instance is available directly. The parsed metadata is also accessible as a Stolt\Ai\Skill\Metadata object.

use Stolt\Ai\Skill\Validator;

$validator = new Validator();
$result = $validator->validateContent('raw-skill-content');

if ($result->isInvalid()) {
    foreach ($result->errors() as $error) {
        echo $error . PHP_EOL;
    }
    // Raw metadata can still be inspected when parsing succeeded but validation failed.
    $rawMetadata = $result->rawMetadata();
    exit(1);
}

// Primary SkillMd abstraction — available on every valid result.
$skillMd = $result->skillMd();  // returns ?SkillMd (null when invalid)

// Or assert the SkillMd directly, which throws a LogicException when the result is invalid.
$skillMd = $result->toSkillMd();

// Use the SkillMd instance.
$name        = $skillMd->name();
$description = $skillMd->description();
$body        = $skillMd->body();
$tags        = $skillMd->tags();
$version     = $skillMd->version();

// Metadata object for field access with defaults.
$metadata    = $result->metadata();
$allowedTools = $metadata?->get('allowed-tools', []);
$model       = $metadata?->get('model');
$effort      = $metadata?->get('effort');

// Markdown instructions after the YAML frontmatter.
$instructions = $result->body();

// Array representation for logging, JSON APIs, or integrations.
$arrayResult = $result->toArray();

echo sprintf('Skill "%s" is valid: %s', $name, $description) . PHP_EOL;

Round-tripping between content and SkillMd

Because validateSkillMd() accepts a SkillMd instance and toSkillMd() returns one, validation results and SkillMd objects round-trip cleanly:

use Stolt\Ai\Skill\Validator;

$validator = new Validator();

// Parse and validate raw content.
$result = $validator->validateContent($rawContent);

// Obtain the primary SkillMd abstraction.
$skillMd = $result->toSkillMd();

// Re-validate the SkillMd — e.g. after modifying it.
$revalidated = $validator->validateSkillMd($skillMd);

For an actual integration, the project list-skills-command can also be consolidated.

Validation rules

The validator checks that a SKILL.md document:

• starts with YAML frontmatter delimited by --- lines,
• contains the required name field,
• contains the required description field,
• uses a non-empty, lowercase, hyphenated skill name,
• contains Markdown instructions after the frontmatter,
• only uses supported frontmatter fields,
• uses lists for list-like fields such as tags, paths, and allowed-tools,
• uses a boolean value for disable-model-invocation.

Supported frontmatter fields include:

• name
• description
• when_to_use
• allowed-tools
• disable-model-invocation
• argument-hint
• arguments
• paths
• model
• effort
• metadata
• compatibility
• license
• author
• version
• tags

Running tests

composer test

License

This library is licensed under the MIT license. Please see LICENSE.md for more details.

Changelog

Please see CHANGELOG.md for more details.

Inspiration

This library idea is inspired by the work on agent-skills-validator by ronaldtebrake.

Contributing

Please see CONTRIBUTING.md for more details.