Agent Skills · Learn · The open SKILL.md standard
The open standard, explained

What is an agent skill?

An agent skill is a SKILL.md file — a plain-markdown instruction set, optionally bundled with scripts and reference files, that a compatible AI coding agent loads only when it's relevant. It's the unit of reusable, portable expertise in the open Agent Skills standard.

The shape of a skill

A skill is a folder containing one required file, SKILL.md, plus anything it needs to do its job:

my-skill/
├── SKILL.md          # YAML frontmatter + markdown instructions
├── scripts/          # optional: helper scripts the agent can run
└── references/       # optional: docs the agent loads on demand

The SKILL.md opens with a small YAML frontmatter block — at minimum a name and a description — followed by the instructions themselves in markdown.

Progressive disclosure — why skills don't bloat context

A compatible agent reads every installed skill's name and description at startup (cheap — a line or two each). It pulls the full SKILL.md into context only when a task matches the description. That's progressive disclosure: you can install hundreds of skills without drowning the model in instructions it doesn't need right now.

An open, cross-agent standard

SKILL.md was originally released by Anthropic and is now maintained as an open standard at agentskills.io. Because the format is just markdown + frontmatter, it isn't tied to any single agent — the same skill can work across Hermes Agent, Cursor, OpenAI Codex, Gemini CLI, OpenCode, Claude Code and 30+ more clients. Some agents read the frontmatter natively; others load the body as a rules or instructions file (see the install guide for each).

Skill vs MCP server vs plugin

A skill is knowledge and instructions — it teaches the model how to do something. An MCP server is tools and data — it gives the model new capabilities to call. They're complementary: a skill can tell the agent how to use an MCP server's tools well.

Frequently asked

What is an agent skill? — answered

Is an agent skill the same as a SKILL.md file?
Yes. "Agent skill" is the concept; SKILL.md is the file that defines it. A skill is a folder whose entry point is a SKILL.md (markdown instructions + YAML frontmatter), optionally with bundled scripts and references.
Do agent skills only work with one AI agent?
No — that's the point of the open standard. A SKILL.md following the agentskills.io format works across many agents. Some load the frontmatter natively; others read the body as a rules or instructions file. The install guide covers each.
Who created the Agent Skills standard?
The SKILL.md format was originally released by Anthropic and is now maintained as an open standard at agentskills.io, adopted across the broader agent ecosystem.