Have you heard "Agent Skill" or just "Skill"? It sounds technical, but a Skill is, in one line, "a folder that records how to do a specific task well for Claude" — much like a recipe card. This article explains what a Skill is and how it works, understandable without any coding knowledge.
What is a Skill? (one-sentence definition)
A Skill is a single folder containing instructions, scripts, and resources. Inside it is a file called SKILL.md (required) that holds the "here's how to do this task" guidance. When your request matches that Skill, Claude opens the folder, reads the guidance, and handles the task better in that way.
An easy analogy: if everyday Claude is "someone who can cook," a Skill is "the recipe card for how we make our family's stew." Hand over that card and it cooks it the same way, more accurately, every time.
What's inside the folder?
The core of a Skill folder is a single SKILL.md file. It usually contains:
- name — the Skill's name.
- description — a line or two on what it does and when to use it. This is the most important part, because Claude uses it to decide "I should use this Skill now."
- body (instructions) — the concrete steps Claude actually follows.
Optionally, a Skill can also include scripts/ (code to run), references/ (reference docs), and assets/ (templates, images). But a single SKILL.md is enough to be a Skill.
How does it work? — "unfold only when needed"
The clever part is that a Skill keeps just its name and description on hand normally, and reads the full content only when a task matches. The technical term is "progressive disclosure." Thanks to this, you can keep many Skills around with almost no footprint when idle.
The flow: (1) normally only the Skill's name/description is held → (2) when your request matches a Skill's description, its full SKILL.md is read → (3) the task is performed per the instructions (loading bundled scripts/resources then, if needed).
Two kinds: pre-built vs. custom
- Pre-built Skills — made in advance by Anthropic; the headline examples are document Skills for PowerPoint, Excel, Word, and PDF. When you make a related request, Claude uses them automatically, so there's usually nothing to install.
- Custom Skills — ones you (or your company) build. Put your brand rules or work procedures in them, and Claude works that way without you re-pasting instructions every time. You can add them in claude.ai settings, Claude Code, the Claude API, and more.
Both kinds work the same way. And Skills are an open standard released by Anthropic, designed so the same format works across other compatible AI tools.
Using them safely
An important caution: since Skills instruct Claude to take new actions, use only Skills from trusted sources (your own, or provided by Anthropic). A Skill of unknown origin could steer Claude to behave contrary to its stated purpose, so review the SKILL.md and bundled files carefully before use. To start, it's safest to begin with pre-built Skills or Anthropic's official examples.
Summary
A Skill isn't a hard technology — it's "a folder (recipe card) that records how to do a specific task well for Claude." The core is a single SKILL.md file, it unfolds only when needed, and there are two kinds: pre-built and custom. To learn more, continue with the Claude skills library — where to get them and using skills by purpose on this site.
This article explains public information from official Anthropic sources (platform.claude.com/docs, anthropic.com, agentskills.io) in beginner-friendly terms. This site is not an official Anthropic site.