An agent skill is a reusable instruction set that teaches an AI agent how to perform a specific task, packaged so you can install it with one command and have the agent pick up the capability.
A skill is essentially expertise written down in a form an agent can load. Instead of re-explaining how you want code reviewed, tests written or SEO audited every time, you install a skill once and the agent follows those instructions whenever the task comes up. A skill is usually a SKILL.md file plus any supporting scripts or templates it needs.
Skills are composable: you can install a whole pack from a repo and let the agent pull in the ones relevant to the current task. Good skills are opinionated and narrow, one clear job done well, which is why a repo often ships dozens of small skills rather than one giant prompt.
They install through the skills CLI with a single command and work across any skills-compatible agent, so the same skill improves Claude Code, Cursor and others alike.
A prompt is a single instruction you paste in. A skill is packaged, versioned and installable, and the agent loads it automatically when relevant, closer to a plugin than a one-off message.
Run the skills CLI command shown on the skill's page, e.g. npx skills add <repo> --skill <name>. The agent then follows its instructions.