skill-writer

What this skill does

# Skill Writer

This Skill helps you create well-structured Agent Skills for Claude Code that follow best practices and validation requirements.

## When to use this Skill

Use this Skill when:

- Creating a new Agent Skill
- Writing or updating SKILL.md files
- Designing skill structure and frontmatter
- Troubleshooting skill discovery issues
- Converting existing prompts or workflows into Skills

## Instructions

### Step 1: Determine Skill scope

First, understand what the Skill should do:

1. **Ask clarifying questions**:

   - What specific capability should this Skill provide?
   - When should Claude use this Skill?
   - What tools or resources does it need?
   - Is this for personal use or team sharing?

2. **Keep it focused**: One Skill = one capability
   - Good: "PDF form filling", "Excel data analysis"
   - Too broad: "Document processing", "Data tools"

### Step 2: Choose Skill location

Determine where to create the Skill:

**Personal Skills** (`~/.claude/skills/`):

- Individual workflows and preferences
- Experimental Skills
- Personal productivity tools

**Project Skills** (`.claude/skills/`):

- Team workflows and conventions
- Project-specific expertise
- Shared utilities (committed to git)

### Step 3: Create Skill structure

Create the directory and files:

```bash
# Personal
mkdir -p ~/.claude/skills/skill-name

# Project
mkdir -p .claude/skills/skill-name
```

For multi-file Skills:

```
skill-name/
├── SKILL.md (required)
├── reference.md (optional)
├── examples.md (optional)
├── scripts/
│   └── helper.py (optional)
└── templates/
    └── template.txt (optional)
```

### Step 4: Write SKILL.md frontmatter

Create YAML frontmatter with required fields:

```yaml
---
name: skill-name
description: Brief description of what this does and when to use it
---
```

**Field requirements**:

- **name**:

  - Lowercase letters, numbers, hyphens only
  - Max 64 characters
  - Must match directory name
  - Good: `pdf-processor`, `git-commit-helper`
  - Bad: `PDF_Processor`, `Git Commits!`

- **description**:
  - Max 1024 characters
  - Include BOTH what it does AND when to use it
  - Use specific trigger words users would say
  - Mention file types, operations, and context

**Optional frontmatter fields**:

- **allowed-tools**: Restrict tool access (comma-separated list)
  ```yaml
  allowed-tools: Read, Grep, Glob
  ```
  Use for:
  - Read-only Skills
  - Security-sensitive workflows
  - Limited-scope operations

### Step 5: Write effective descriptions

The description is critical for Claude to discover your Skill.

**Formula**: `[What it does] + [When to use it] + [Key triggers]`

**Examples**:

✅ **Good**:

```yaml
description: 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.
```

✅ **Good**:

```yaml
description: Analyze Excel spreadsheets, create pivot tables, and generate charts. Use when working with Excel files, spreadsheets, or analyzing tabular data in .xlsx format.
```

❌ **Too vague**:

```yaml
description: Helps with documents
description: For data analysis
```

**Tips**:

- Include specific file extensions (.pdf, .xlsx, .json)
- Mention common user phrases ("analyze", "extract", "generate")
- List concrete operations (not generic verbs)
- Add context clues ("Use when...", "For...")

### Step 6: Structure the Skill content

Use clear Markdown sections:

````markdown
# Skill Name

Brief overview of what this Skill does.

## Quick start

Provide a simple example to get started immediately.

## Instructions

Step-by-step guidance for Claude:

1. First step with clear action
2. Second step with expected outcome
3. Handle edge cases

## Examples

Show concrete usage examples with code or commands.

## Best practices

- Key conventions to follow
- Common pitfalls to avoid
- When to use vs. not use

## Requirements

List any dependencies or prerequisites:

```bash
pip install package-name
```
````

## Advanced usage

For complex scenarios, see [reference.md](reference.md).

````

### Step 7: Add supporting files (optional)

Create additional files for progressive disclosure:

**reference.md**: Detailed API docs, advanced options
**examples.md**: Extended examples and use cases
**scripts/**: Helper scripts and utilities
**templates/**: File templates or boilerplate

Reference them from SKILL.md:
```markdown
For advanced usage, see [reference.md](reference.md).

Run the helper script:
\`\`\`bash
python scripts/helper.py input.txt
\`\`\`
````

### Step 8: Validate the Skill

Check these requirements:

✅ **File structure**:

- [ ] SKILL.md exists in correct location
- [ ] Directory name matches frontmatter `name`

✅ **YAML frontmatter**:

- [ ] Opening `---` on line 1
- [ ] Closing `---` before content
- [ ] Valid YAML (no tabs, correct indentation)
- [ ] `name` follows naming rules
- [ ] `description` is specific and < 1024 chars

✅ **Content quality**:

- [ ] Clear instructions for Claude
- [ ] Concrete examples provided
- [ ] Edge cases handled
- [ ] Dependencies listed (if any)

✅ **Testing**:

- [ ] Description matches user questions
- [ ] Skill activates on relevant queries
- [ ] Instructions are clear and actionable

### Step 9: Test the Skill

1. **Restart Claude Code** (if running) to load the Skill

2. **Ask relevant questions** that match the description:

   ```
   Can you help me extract text from this PDF?
   ```

3. **Verify activation**: Claude should use the Skill automatically

4. **Check behavior**: Confirm Claude follows the instructions correctly

### Step 10: Debug if needed

If Claude doesn't use the Skill:

1. **Make description more specific**:

   - Add trigger words
   - Include file types
   - Mention common user phrases

2. **Check file location**:

   ```bash
   ls ~/.claude/skills/skill-name/SKILL.md
   ls .claude/skills/skill-name/SKILL.md
   ```

3. **Validate YAML**:

   ```bash
   cat SKILL.md | head -n 10
   ```

4. **Run debug mode**:
   ```bash
   claude --debug
   ```

## Common patterns

### Read-only Skill

```yaml
---
name: code-reader
description: Read and analyze code without making changes. Use for code review, understanding codebases, or documentation.
allowed-tools: Read, Grep, Glob
---
```

### Script-based Skill

```yaml
---
name: data-processor
description: Process CSV and JSON data files with Python scripts. Use when analyzing data files or transforming datasets.
---

# Data Processor

## Instructions

1. Use the processing script:
\`\`\`bash
python scripts/process.py input.csv --output results.json
\`\`\`

2. Validate output with:
\`\`\`bash
python scripts/validate.py results.json
\`\`\`
```

### Multi-file Skill with progressive disclosure

```yaml
---
name: api-designer
description: Design REST APIs following best practices. Use when creating API endpoints, designing routes, or planning API architecture.
---

# API Designer

Quick start: See [examples.md](examples.md)

Detailed reference: See [reference.md](reference.md)

## Instructions

1. Gather requirements
2. Design endpoints (see examples.md)
3. Document with OpenAPI spec
4. Review against best practices (see reference.md)
```

## Best practices for Skill authors

1. **One Skill, one purpose**: Don't create mega-Skills
2. **Specific descriptions**: Include trigger words users will say
3. **Clear instructions**: Write for Claude, not humans
4. **Concrete examples**: Show real code, not pseudocode
5. **List dependencies**: Mention required packages in description
6. **Test with teammates**: Verify activation and clarity
7. **Version your Skills**: Document changes in content
8. **Use progressive disclosure**: Put advanced details in separate files

## Validation checklist

Before finalizing a Skill, verify:

- [ ] Name is lowercase, hyphens only, max 64 chars
- [ ] Description is specific and < 1024 chars
- [ ] Description includes "what" and "when"
- [ ] YAML frontmatter is valid
- [ ] Instructions are step-by-step