writing-skills

What this skill does

# Writing Skills

## Overview

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

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 `requirements-framework: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 `references/skill-authoring-best-practices.md`. That 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 Claude instances 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 |

## 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 CLAUDE.md)
- 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

## Directory Structure (Requirements Framework Convention)

```
plugins/requirements-framework/skills/
  skill-name/
    SKILL.md              # Main reference (required)
    references/           # Supporting files subdirectory
      supporting-file.md  # Only if needed
```

**Key conventions for this framework:**
- Supporting files go in a `references/` subdirectory (not flat alongside SKILL.md)
- YAML frontmatter includes `git_hash` field for version tracking
- Skills that satisfy requirements include a "Requirements Integration" section

**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):**
- Required fields: `name`, `description`, `git_hash`
- Max 1024 characters for name + description combined
- `name`: Use letters, numbers, and hyphens only (no parentheses, special chars)
- `description`: Third-person, describes ONLY when to use (NOT what it does)
  - Start with "Use when..." to focus on triggering conditions
  - Include specific symptoms, situations, and contexts
  - **NEVER summarize the skill's process or workflow** (see CSO section for why)
  - Keep under 500 characters if possible
- `git_hash`: Set to `uncommitted` for new files; updated by `./update-plugin-versions.sh`

```markdown
---
name: Skill-Name-With-Hyphens
description: Use when [specific triggering conditions and symptoms]
git_hash: uncommitted
---

# Skill Name

## Overview
What is this? Core principle in 1-2 sentences.

## When to Use
[Small inline flowchart IF decision non-obvious]

Bullet list with SYMPTOMS and use cases
When NOT to use

## Core Pattern (for techniques/patterns)
Before/after code comparison

## Quick Reference
Table or bullets for scanning common operations

## Implementation
Inline code for simple patterns
Link to file for heavy reference or reusable tools

## Requirements Integration (if applicable)
How this skill interacts with the requirements system:
- Which requirement it satisfies (satisfied_by_skill mapping)
- Auto-satisfy behavior
- Chaining to next skill

## Common Mistakes
What goes wrong + fixes
```

## Claude Search Optimization (CSO)

**Critical for discovery:** Future Claude needs to FIND your skill.

### 1. Rich Description Field

**Purpose:** Claude reads description to decide which skills to load for a given task. Make it answer: "Should I read this skill right now?"

**Format:** Start with "Use when..." to focus on triggering conditions.

**CRITICAL: Description = When to Use, NOT What the Skill Does**

The description should ONLY describe triggering conditions. Do NOT summarize the skill's process or workflow in the description.

**Why this matters:** Testing revealed that when a description summarizes the skill's workflow, Claude may follow the description instead of reading the full skill content. A description saying "code review between tasks" caused Claude to do ONE review, even though the skill's flowchart clearly showed TWO reviews (spec compliance then code quality).

When the description was changed to just "Use when executing implementation plans with independent tasks" (no workflow summary), Claude correctly read the flowchart and followed the two-stage review process.

**The trap:** Descriptions that summarize workflow create a shortcut Claude will take. The skill body becomes documentation Claude skips.

```yaml
# BAD: Summarizes workflow - Claude may follow this instead of reading skill
description: Use when executing plans - dispatches subagent per task with code review between tasks

# BAD: Too much process detail
description: Use for TDD - write test first, watch it fail, write minimal code, refactor

# GOOD: Just triggering conditions, no workflow summary
description: Use when executing implementation plans with independent tasks in the current session

# GOOD: Triggering conditions only
description: Use when implementing any feature or bugfix, before writing implementation code
```

**Content:**
- Use concrete triggers, symptoms, and situations that signal this skill applies
- Describe the *problem* (race conditions, inconsistent behavior) not *language-specific symptoms* (setTimeout, sleep)
- Keep triggers technology-agnostic unless the skill itself is technology-specific
- Write in third person (injected into system prompt)
- **NEVER summarize the skill's process or workflow**

### 2. Keyword Coverage

Use words Claude would search for:
- Error messages: "Hook timed out", "ENOTEMPTY", "race condition"
- Symptoms: "flaky", "hanging", "zombie", "pollution"
- Synonyms: "timeout/hang/freeze", "cleanup/teardown/afterEach"
- Tools: Actual commands, library names, file types

### 3. Descriptive Naming

**Use active voice, verb-first:**
- `creating-skills` not `skill-creation`
- `condition-based-waiting` not `async-test-helpers`

**Gerunds (-ing) work well for processes:**
- `creating-skills`, `testing-skills`, `debugging-with-logs`
- Active, describes the action you're taking

### 4. Token Efficiency (Critical)

**Problem:** Bootstrap and frequently-referenced skills load into EVERY conversation. Every token counts.

**Target word counts:**
- Bootstrap/frequently-loaded skills: < 200