Agent Skills (agentskills.io)
Create portable skills for AI agents. Works with Claude Code, Cursor, GitHub Copilot, OpenAI integrations, VS Code (symlinks enable sharing across tools).
Resources
- Specification: https://agentskills.io/specification | Validator: https://github.com/agentskills/agentskills
Structure
skill-name/
├── SKILL.md # Required (frontmatter + instructions, <5000 tokens activation)
├── scripts/ # Optional: executable code
├── references/ # Optional: detailed docs
└── assets/ # Optional: templates, static files
Rules: Dir name = frontmatter name:. Only 3 subdirs. SKILL.md <500 lines. ~100 tokens for discovery (name+desc).
Frontmatter
Required
name: 1-64 chars, lowercase alphanumeric-hyphens (^[a-z0-9]+(-[a-z0-9]+)*$)description: 1-1024 chars, include "Use when..." (discovery budget: ~100 tokens)
Optional
license: SPDX identifier (Apache-2.0, MIT) |compatibility: Environment reqs (<500 chars)metadata: Key-value pairs (author, version, tags) |allowed-tools: Space-delimited tool list
Validation
# Install permanently (vs ephemeral uvx)
uv tool install git+https://github.com/agentskills/agentskills#subdirectory=skills-ref
# Or use uvx for one-shot validation
uvx --from git+https://github.com/agentskills/agentskills#subdirectory=skills-ref skills-ref validate ./skill
| Command | Description |
|---|---|
skills-ref validate <path> |
Check structure, frontmatter, token budgets |
skills-ref read-properties <path> |
Extract metadata |
skills-ref to-prompt <path> |
Generate prompt format |
Writing Rules
- Imperative language: "Check:
command" not "You might want to..." - Concrete examples with expected output; handle common errors with solutions
- Progressive disclosure: core in SKILL.md (<5000 tokens), details in references/
Common Errors
| Error | Fix |
|---|---|
| Invalid name | Lowercase alphanumeric-hyphens only |
| Missing description | Add description: field with "Use when..." |
| Description too long | <1024 chars, move details to body |
| Invalid YAML | Check indentation, quote special chars |
| Missing SKILL.md | Filename must be exactly SKILL.md |
| Dir name mismatch | Directory name must match name: field |
Quick Workflow
- Create:
mkdir skill-name && touch skill-name/SKILL.md - Add frontmatter (name, description with "Use when...")
- Write instructions (bullets, not prose); validate:
skills-ref validate ./skill-name - Test with AI agent, iterate; add LICENSE, push to repository
Plugin Structure (Claude Code)
plugin-name/
├── .claude-plugin/plugin.json
├── README.md, LICENSE, CHANGELOG.md # CHANGELOG.md tracks versions
├── skills/skill-name/SKILL.md
├── agents/ # Optional: subagents (.md files)
└── examples/ # Optional: full demo projects
Distinctions: Plugin examples/ = runnable projects. Skill assets/ = static resources only.
Batch Validation & Versioning
bash scripts/validate-skills-repo.sh # Validate all skills in repo
bash scripts/bump-changed-plugins.sh # Auto-bump only changed plugins (semver)
Minimal Example
---
name: example-skill
description: Brief description. Use when doing X.
---
# Example Skill
## Prerequisites
- Required tools
## Instructions
1. First step: `command`
2. Second step with example
## Troubleshooting
**Error**: Message → **Fix**: Solution
Symlink Sharing
Share skills across Claude Code, Cursor, VS Code: ln -s /path/to/skills ~/.cursor/skills
References
- specification.md - Full YAML schema, token budgets
- examples.md - Complete examples across platforms
- validation.md - Error troubleshooting
- best-practices.md - Advanced patterns, symlink setup