WTF is Agent Skills?
Folders of instructions, scripts and resources that an agent loads only when a task needs them.
Also called: skills, skill.md
TL;DR
Rather than stuffing every instruction into one giant prompt, you package know-how ("how we make slide decks", "how to fill this PDF form") as a skill. The agent sees a short description of each skill and pulls in the full contents only when relevant.
How it works
A skill is a directory with a SKILL.md file (YAML frontmatter with a name and description, then Markdown instructions) plus optional scripts and reference files. Only the name and description sit in context by default; the agent reads the rest on demand. This progressive disclosure keeps the context small while letting an agent carry many specialised capabilities. Skills complement MCP: MCP provides access to tools, skills provide the procedural knowledge of how to use them well.
Example
---
name: release-notes
description: Write release notes from merged PRs. Use when asked for a changelog.
---
1. List PRs merged since the last tag.
2. Group them into Features, Fixes, Chores.
3. Write one line per PR in plain English.Origin
- Coined / introduced by
- Anthropic
- When
- 16 Oct 2025
- Story
- Introduced by Anthropic, later published as an open format used by other agent tools.