skill

Creating Skills & Commands

This skill teaches how to create effective Claude Code skills following the official specification. It combines spec-driven creation with TDD-adapted pressure testing.

Commands and Skills Are Now The Same Thing

Custom slash commands have been merged into skills. A file at .claude/commands/review.md and a skill at .claude/skills/review/SKILL.md both create /review and work the same way. Existing .claude/commands/ files keep working. Skills add optional features: a directory for supporting files, frontmatter to control invocation, and automatic context loading.

If a skill and a command share the same name, the skill takes precedence.

When To Create What

Use a command file (commands/name.md) when:

• Simple, single-file workflow
• No supporting files needed
• Task-oriented action (deploy, commit, triage)

Use a skill directory (skills/name/SKILL.md) when:

• Need supporting reference files, scripts, or templates
• Background knowledge Claude should auto-load
• Complex enough to benefit from progressive disclosure

Both use identical YAML frontmatter and markdown content format.

Standard Markdown Format

Use YAML frontmatter + markdown body with standard markdown headings. Keep it clean and direct.

---
name: my-skill-name
description: What it does and when to use it
---

# My Skill Name

## Quick Start
Immediate actionable guidance...

## Instructions
Step-by-step procedures...

## Examples
Concrete usage examples...

Frontmatter Reference

All fields are optional. Only description is recommended.

Field	Required	Description
name	No	Display name. Lowercase letters, numbers, hyphens (max 64 chars). Defaults to directory name.
description	Recommended	What it does AND when to use it. Claude uses this for auto-discovery. Max 1024 chars.
argument-hint	No	Hint shown during autocomplete. Example: [issue-number]
disable-model-invocation	No	Set true to prevent Claude auto-loading. Use for manual workflows like /deploy, /commit. Default: false.
user-invocable	No	Set false to hide from / menu. Use for background knowledge. Default: true.
allowed-tools	No	Tools Claude can use without permission prompts. Example: Read, Bash(git *)
model	No	Model to use. Options: haiku, sonnet, opus.
context	No	Set fork to run in isolated subagent context.
agent	No	Subagent type when context: fork. Options: Explore, Plan, general-purpose, or custom agent name.

Invocation Control

Frontmatter	User can invoke	Claude can invoke	When loaded
(default)	Yes	Yes	Description always in context, full content loads when invoked
disable-model-invocation: true	Yes	No	Description not in context, loads only when user invokes
user-invocable: false	No	Yes	Description always in context, loads when relevant

Use disable-model-invocation: true for workflows with side effects: /deploy, /commit, /triage-prs, /send-slack-message. You don't want Claude deciding to deploy because your code looks ready.

Use user-invocable: false for background knowledge that isn't a meaningful user action: coding conventions, domain context, legacy system docs.

Dynamic Features

Arguments

Use $ARGUMENTS placeholder for user input. If not present in content, arguments are appended automatically.

Access individual args: $ARGUMENTS[0] or shorthand $0, $1, $2.

Dynamic Context Injection

The !`command` syntax runs shell commands before content is sent to Claude.

Running in a Subagent

Add context: fork to run in isolation. The skill content becomes the subagent's prompt.

Progressive Disclosure

Keep SKILL.md under 500 lines. Split detailed content into reference files:

my-skill/
├── SKILL.md           # Entry point (required, overview + navigation)
├── reference.md       # Detailed docs (loaded when needed)
├── examples.md        # Usage examples (loaded when needed)
└── scripts/
    └── helper.py      # Utility script (executed, not loaded)

Keep references one level deep from SKILL.md.

What Would You Like To Do?

1. Create new skill — Build from scratch (Phase 1: Spec → Phase 2: TDD Test)
2. Create new command — Build a slash command
3. Audit existing skill — Check against best practices (use /interskill:audit)
4. Add component — Add workflow/reference/example
5. Get guidance — Understand skill design

Creating a New Skill

Phase 1: Spec-Driven Creation

Follow workflows/create-new-skill.md for the full step-by-step process.

Quick summary:

1. Choose type (command vs skill, manual vs background)
2. Write frontmatter (name, description, invocation control)
3. Write body with standard markdown headings
4. Add reference files if needed
5. Link references from SKILL.md

Phase 2: TDD Pressure Testing

After creating the skill, validate it using TDD-adapted testing. See references/testing-skills-with-subagents.md for the full methodology.

Core principle: If you didn't watch an agent fail without the skill, you don't know if the skill teaches the right thing.

Quick summary:

1. RED — Run a pressure scenario with a subagent without the skill. Document exact rationalizations the agent uses to deviate.
2. GREEN — Load the skill and re-run. Verify the agent now complies.
3. REFACTOR — Find new rationalizations, plug loopholes, re-verify.

Effective Descriptions

The description enables skill discovery. Include both what it does and when to use it.

Good: "Extract text and tables from PDF files, fill forms, merge documents. Use when working with PDF files or when the user mentions PDFs, forms, or document extraction."

Bad: "Helps with documents"

Anti-Patterns to Avoid

• XML tags in body — Use standard markdown headings
• Vague descriptions — Be specific with trigger keywords
• Deep nesting — Keep references one level from SKILL.md
• Missing invocation control — Side-effect workflows need disable-model-invocation: true
• Too many options — Provide a default with escape hatch
• Punting to Claude — Scripts should handle errors explicitly

Reference Files

For detailed guidance, see:

• official-spec.md — Official skill specification
• best-practices.md — Skill authoring best practices
• anthropic-best-practices.md — Anthropic's official guidance
• testing-skills-with-subagents.md — TDD pressure testing
• persuasion-principles.md — Skill persuasion patterns
• claude-search-optimization.md — CSO for skill discovery