Skills Dev

Skills Development

Create skills that follow the Agent Skills specification—an open format supported by Claude Code, Cursor, VS Code, GitHub Copilot, Codex, and other agent products.

Workflow

1. Discovery — Understand what the skill should do
2. Archetype Selection — Choose the best pattern
3. Initialization — Create skill structure
4. Customization — Tailor to specific needs
5. Validation — Verify quality before committing

Stage 1: Discovery

Ask about the skill:

• What problem does this skill solve?
• What are the main capabilities?
• What triggers should invoke it? (phrases users would say)
• Where should it live? (personal, project, or plugin)

Stage 2: Archetype Selection

Stage 3: Directory Structure

skill-name/
├── SKILL.md           # Required: instructions + metadata
├── scripts/           # Optional: executable code
├── references/        # Optional: documentation
└── assets/            # Optional: templates, resources

Stage 4: Frontmatter Schema

---
name: skill-name
description: What it does and when to use it. Include trigger keywords.
version: 1.0.0                         # optional, recommended
license: Apache-2.0                    # optional
compatibility: Requires git and jq     # optional
metadata:                              # optional
  author: your-org
  category: development
  tags: [testing, automation]
---

Note: Platform-specific fields (e.g., Claude's allowed-tools, user-invocable) should be added per-platform. See claude-code.md for Claude Code extensions.

Custom Frontmatter

Custom fields must be nested under metadata:

---
name: my-skill
description: ...
metadata:
  author: your-org
  version: "1.0"
  category: development
  tags: [typescript, testing]
---

Top-level custom fields are not allowed and may cause parsing errors.

Description Formula

[WHAT] + [WHEN] + [TRIGGERS]

description: Extracts text and tables from PDF files, fills forms, merges documents. Use when working with PDF files or when the user mentions PDFs, forms, or document extraction.

Checklist:

• Explains WHAT (capabilities)
• States WHEN (trigger conditions)
• Includes 3-5 trigger KEYWORDS
• Uses third-person voice
• Under 200 words

Stage 5: Validation

Validation Checklist

A. YAML Frontmatter

• Opens with --- on line 1, closes with ---
• name and description present (required)
• Uses spaces, not tabs
• Special characters quoted

B. Naming

• Lowercase, numbers, hyphens only (1-64 chars)
• Matches parent directory name
• No --, leading/trailing hyphens
• No anthropic or claude in name

C. Description Quality

• WHAT: Explains capabilities
• WHEN: States "Use when..." conditions
• TRIGGERS: 3-5 keywords users would say
• Third-person voice (not "I can" or "you can")

D. Structure

• SKILL.md under 500 lines
• All referenced files exist
• No TODO/placeholder markers
• Progressive disclosure (details in references/)

Report Format

# Skill Check: {skill-name}

**Status**: PASS | WARNINGS | FAIL
**Issues**: {critical} critical, {warnings} warnings

## Critical (must fix)
1. {issue with fix}

## Warnings (should fix)
1. {issue with fix}

## Strengths
- {what's done well}

Core Principles

Concise is key

Context window is shared. Only include what the agent doesn't already know. Challenge each paragraph—does it justify its token cost?

Third-person descriptions

Descriptions inject into system prompt:

• "Extracts text from PDFs"
• "I can help you extract text from PDFs"

Progressive disclosure

Keep SKILL.md under 500 lines. Move details to:

• references/ - Detailed docs, API references
• scripts/ - Executable utilities (code never enters context)
• assets/ - Templates, data files

Token loading:

1. Metadata (~100 tokens): name + description at startup
2. Instructions (<5000 tokens): SKILL.md body when activated
3. Resources (as needed): files loaded only when referenced

Degrees of freedom

Match instruction specificity to task requirements:

• High freedom (text): Multiple valid approaches, use judgment
• Medium freedom (pseudocode): Preferred pattern with variation allowed
• Low freedom (scripts): Exact sequence required, no deviation

See patterns.md for detailed examples.

Naming Requirements

• Lowercase letters, numbers, hyphens only
• Cannot start/end with hyphen or contain --
• Must match parent directory name
• Cannot contain anthropic or claude

Recommended: Gerund form (processing-pdfs, reviewing-code)

Platform-Specific Guidance

Skills are cross-platform, but each tool has specific implementation details:

• Claude Code: See claude-code.md for tool restrictions, testing, troubleshooting, and Claude-specific frontmatter extensions
• Codex CLI: See codex.md for discovery paths, $skill-name invocation

See implementations.md for storage paths and invocations.md for activation patterns.

References

• steps-pattern.md - Composable skill workflows with dependencies
• patterns.md - Degrees of freedom, script design, variant organization
• best-practices.md - Community patterns, testing strategies
• quick-reference.md - Fast checklist and one-liners
• implementations.md - Per-tool storage paths
• invocations.md - How tools activate skills
• compatibility.md - Path compatibility matrix

External Resources

• Agent Skills Specification
• Best Practices Guide
• skills-ref Validation Library