Skill Writer

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:

# 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:

---
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)

  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:

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:

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:

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:

# 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.

### 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