# Filesystem-Based Agent Skills A filesystem-based agent skill is a reusable directory containing instructions and, optionally, scripts, references, fixtures, and assets. A host can discover the skill from metadata, load its full instructions when relevant, and execute or read supporting resources only as needed. Shazam and XApps are not historical agent-skill systems, but their capability-per-file organization, stable names, generated discovery surfaces, and self-contained folders anticipate the same packaging instinct. Related: [[wiki/Capability Discovery|Capability Discovery]], [[wiki/Progressive Disclosure|Progressive Disclosure]], [[wiki/Plugin Architecture|Plugin Architecture]], [[projects/Shazam - A Portable Perl Capability Library|Shazam]]. Sources: [OpenAI — Agent Skills](https://developers.openai.com/codex/skills), [Anthropic — Agent Skills](https://docs.anthropic.com/en/docs/agents-and-tools/agent-skills/overview)