Agent Skills Specification 🧩 Skill Open source

What it does

This is the home of the Agent Skills open format: the specification, the documentation behind agentskills.io and a small reference library. Anthropic first developed the format and later released it as an open standard. The repository does not ship ready-made skills for daily coding work. It defines what a skill is, so that one skill folder works in any agent that supports the standard.

In short, a skill is a folder with a SKILL.md file. The file starts with metadata (at least a name and a description), followed by instructions. The folder can also include scripts, references and assets. Agents load skills in three stages: they read only names and descriptions at startup, load the full instructions when a task matches, and then run any bundled code or files as needed.

What is inside

• Documentation: the source of the agentskills.io guides and the format specification.
• skills-ref: a Python reference library and CLI that validates a skill folder, reads its properties as JSON, and generates the <available_skills> block that agents put in their prompt. The README says it is for demonstration and not for production use.
• Contribution guides: how the wider ecosystem proposes changes to the standard.

Works with

The format is supported by many agents and clients, listed in the client showcase on agentskills.io. That includes the major coding agents covered on this site.

How to install

There is nothing to install for everyday use. To try the validator, set up skills-ref from a clone as its README describes, then run:

skills-ref validate path/to/skill
skills-ref to-prompt path/to/skill-a path/to/skill-b

Maintenance and safety

The code is Apache 2.0 and the documentation is CC-BY-4.0. The repository is maintained in the open with a Discord community. It contains no executable skills. The specification itself notes that skills can bundle scripts, so review any skill you install.

Who should use it

Skill authors, tool builders adding skill support to an agent, and anyone who wants the authoritative definition of the SKILL.md format before they write or check their own skills.