This page documents the Agent Skills standard: what it defines, where its canonical text is hosted, how the local spec/ directory relates to it, and how the anthropics/skills repository implements the standard. For details about the SKILL.md file format that the standard mandates, see SKILL.md Format Specification. For how skills are distributed to users, see Platform Integration.
The Agent Skills standard is an open specification that defines how AI agents discover, load, and execute skill modules. It establishes the contract between:
SKILL.md files and supporting scripts.The standard specifies at minimum:
| Concern | What the standard defines |
|---|---|
| Skill identity | The name field format (kebab-case, max 64 chars) |
| Skill discovery | The description field used for trigger matching |
| Skill content | The YAML frontmatter + Markdown body structure of SKILL.md |
| Optional metadata | allowed-tools, license, compatibility, and other optional fields |
The authoritative text of the Agent Skills specification is hosted externally. The local file in this repository, spec/agent-skills-spec.md, is a redirect pointer:
This file contains no specification text itself. It simply directs readers to the external canonical source. The README.md reinforces this with a prominent note at the top:
The spec/ directory exists in the repository to provide a stable local entry point for tooling or contributors who look for the spec relative to the code, without duplicating content that is authoritatively maintained externally.
Diagram: How the Spec Relates to the Repository Implementation
Sources: spec/agent-skills-spec.md, README.md
The anthropics/skills repository is a conforming implementation of the Agent Skills standard. Every skill in skills/ is structured as a directory containing a SKILL.md file whose frontmatter and body follow the standard's format.
Diagram: Standard Fields to Repository Code Entities
Sources: README.md, spec/agent-skills-spec.md
The table below describes the implementation choices this repository makes for each area the standard governs.
| Standard area | Implementation in this repo |
|---|---|
| Spec redirect | spec/agent-skills-spec.md points to agentskills.io/specification |
| Skill format | Every skills/*/SKILL.md has YAML frontmatter with name and description |
| Validation tooling | template/quick_validate.py checks conformance locally |
| Reference template | template/ provides a minimal conforming SKILL.md skeleton |
| Distribution | Skills are bundled as document-skills and example-skills in .claude-plugin/marketplace.json |
| Runtime | Claude dynamically loads the matching SKILL.md based on the description field at invocation time |
For a complete description of the SKILL.md format and all field constraints, see SKILL.md Format Specification. For how the plugin registry bundles skills for distribution, see Marketplace and Plugin System. For validation rules enforced in code, see Skill Validation.
Sources: README.md:1-1, spec/agent-skills-spec.md:1-4
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