writing-skills

The saved excerpt is a snapshot from when this skill was listed. The external source remains the complete and most current version.

---
name: writing-skills
description: Use when creating new skills, editing existing skills, or verifying skills work before deployment
---

# Writing Skills

## Overview

**Writing skills IS Test-Driven Development applied to process documentation.**

**Personal skills live in your runtime's skills directory** (`~/.claude/skills/` on Claude Code) — see [codex-tools.md](../using-superpowers/references/codex-tools.md) or [gemini-tools.md](../using-superpowers/references/gemini-tools.md) for the path on those runtimes. Codex, Copilot CLI, and Gemini CLI all also recognize `~/.agents/skills/` as a cross-runtime alias.

You write test cases (pressure scenarios with subagents), watch them fail (baseline behavior), write the skill (documentation), watch tests pass (agents comply), and refactor (close loopholes).

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

**REQUIRED BACKGROUND:** You MUST understand superpowers:test-driven-development before using this skill. That skill defines the fundamental RED-GREEN-REFACTOR cycle. This skill adapts TDD to documentation.

**Official guidance:** For Anthropic's official skill authoring best practices, see anthropic-best-practices.md. This document provides additional patterns and guidelines that complement the TDD-focused approach in this skill.

## What is a Skill?

A **skill** is a reference guide for proven techniques, patterns, or tools. Skills help future agents find and apply effective approaches.

**Skills are:** Reusable techniques, patterns, tools, reference guides

**Skills are NOT:** Narratives about how you solved a problem once

## TDD Mapping for Skills

| TDD Concept | Skill Creation |
|-------------|----------------|
| **Test case** | Pressure scenario with subagent |
| **Production code** | Skill document (SKILL.md) |
| **Test fails (RED)** | Agent violates rule without skill (baseline) |
| **Test passes (GREEN)** | Agent complies with skill present |
| **Refactor** | Close loopholes while maintaining compliance |
| **Write test first** | Run baseline scenario BEFORE writing skill |
| **Watch it fail** | Document exact rationalizations agent uses |
| **Minimal code** | Write skill addressing those specific violations |
| **Watch it pass** | Verify agent now complies |
| **Refactor cycle** | Find new rationalizations → plug → re-verify |

The entire skill creation process follows RED-GREEN-REFACTOR.

## When to Create a Skill

**Create when:**
- Technique wasn't intuitively obvious to you
- You'd reference this again across projects
- Pattern applies broadly (not project-specific)
- Others would benefit

**Don't create for:**
- One-off solutions
- Standard practices well-documented elsewhere
- Project-specific conventions (put in your instructions file)
- Mechanical constraints (if it's enforceable with regex/validation, automate it—save documentation for judgment calls)

## Skill Types

### Technique
Concrete method with steps to follow (condition-based-waiting, root-cause-tracing)

### Pattern
Way of thinking about problems (flatten-with-flags, test-invariants)

### Reference
API docs, syntax guides, tool documentation (office docs)

## Directory Structure


```
skills/
  skill-name/
    SKILL.md              # Main reference (required)
    supporting-file.*     # Only if needed
```

**Flat namespace** - all skills in one searchable namespace

**Separate files for:**
1. **Heavy reference** (100+ lines) - API docs, comprehensive syntax
2. **Reusable tools** - Scripts, utilities, templates

**Keep inline:**
- Principles and concepts
- Code patterns (< 50 lines)
- Everything else

## SKILL.md Structure

**Frontmatter (YAML):**
- Two required fields: `name` and `description` (see [agentskills.io/specification](https://agentskills.io/specification) for all supported fields)
- Max 1024 characters total
- `name`: Use letters, numbers, and hyphens only (no parentheses, special chars)
- `description`: Thi