Source Code

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

agentskills-io