The agent-frontmatter library is a TypeScript tool designed for parsing, validating, and discovering AI agent files with YAML frontmatter metadata. Key features include YAML frontmatter parsing, comprehensive schema validation with informative error messages, and agent discovery through search and filtering by capabilities, languages, and frameworks. It supports semantic versioning and includes a command-line interface for validation, linting, and information display. Additionally, it offers native file type registration for .agent files on macOS with Quick Look preview capabilities. Users can define agents in Markdown files with specific metadata and utilize parser functions for validation and searching. Installation is available via npm or yarn, with specific commands for macOS registration. The library also includes features for maintaining version compatibility and managing various agent configurations, making it a versatile tool for developers working with AI agents. Contributions and issue tracking can be managed through GitHub.