The Prompt Card Index
Anthropic's Agent Skills repo: the spec and template for your own Claude skills
Anthropic's official repository of Agent Skills, the reusable instruction folders Claude loads on demand, plus the Skills spec and a template for building your own marketing skills.
A Claude Agent Skill is a folder of instructions, scripts and resources that Claude loads dynamically when a task calls for it, rather than carrying every capability in context all the time. This repository is Anthropic's own reference implementation of that idea: the working skills the company itself ships, plus the spec that defines what a valid skill folder looks like.
Why it made the cut
For anyone building their own domain skills, this is the canonical place to start rather than reverse-engineering the format from third-party examples. It is a genuinely large, actively maintained repository, well past a hundred thousand stars and tens of thousands of forks, with heavy ongoing activity, so the spec it documents is the one Claude's own tooling is built against, not a snapshot that has drifted out of date.
How to use it
Install it via /plugin marketplace add anthropics/skills inside Claude, or clone the repository directly to read the spec and the included template before writing a skill of your own. The template is the fastest route to a first working skill: copy its structure, YAML frontmatter and folder layout, then swap in your own domain instructions.
Worth knowing
Most of the repository is Apache-2.0, but the document skills covering docx, pdf, pptx and xlsx are source-available rather than open source, worth checking before you build on top of those specific ones. If you want a worked example of what a marketing skill looks like once written to this spec, the house Google Ads audit Skill on this shelf is packaged exactly this way.