Creating Agent Skills
This skill teaches how to create effective Claude Code Skills following Anthropic's official specification.
Core Principles
- Skills Are Prompts
All prompting best practices apply. Be clear, be direct. Assume Claude is smart - only add context Claude doesn't have.
- Standard Markdown Format
Use YAML frontmatter + markdown body. No XML tags - use standard markdown headings.
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...
- Progressive Disclosure
Keep SKILL.md under 500 lines. Split detailed content into reference files. Load only what's needed.
my-skill/ ├── SKILL.md # Entry point (required) ├── reference.md # Detailed docs (loaded when needed) ├── examples.md # Usage examples └── scripts/ # Utility scripts (executed, not loaded)
- Effective Descriptions
The description field enables skill discovery. Include both what the skill does AND when to use it. Write in third person.
Good:
description: Extracts text and tables from PDF files, fills forms, merges documents. Use when working with PDF files or when the user mentions PDFs, forms, or document extraction.
Bad:
description: Helps with documents
Skill Structure
Required Frontmatter
Field Required Max Length Description
name
Yes 64 chars Lowercase letters, numbers, hyphens only
description
Yes 1024 chars What it does AND when to use it
allowed-tools
No
Tools Claude can use without asking
model
No
Specific model to use
Naming Conventions
Use gerund form (verb + -ing) for skill names:
-
processing-pdfs
-
analyzing-spreadsheets
-
generating-commit-messages
-
reviewing-code
Avoid: helper , utils , tools , anthropic-* , claude-*
Body Structure
Use standard markdown headings:
Skill Name
Quick Start
Fastest path to value...
Instructions
Core guidance Claude follows...
Examples
Input/output pairs showing expected behavior...
Advanced Features
Additional capabilities (link to reference files)...
Guidelines
Rules and constraints...
What Would You Like To Do?
-
Create new skill - Build from scratch
-
Audit existing skill - Check against best practices
-
Add component - Add workflow/reference/example
-
Get guidance - Understand skill design
Creating a New Skill
Step 1: Choose Type
Simple skill (single file):
-
Under 500 lines
-
Self-contained guidance
-
No complex workflows
Progressive disclosure skill (multiple files):
-
SKILL.md as overview
-
Reference files for detailed docs
-
Scripts for utilities
Step 2: Create SKILL.md
name: your-skill-name description: [What it does]. Use when [trigger conditions].
Your Skill Name
Quick Start
[Immediate actionable example]
[Code example]
Instructions
[Core guidance]
Examples
Example 1:
Input: [description]
Output:
[result]
Guidelines
- [Constraint 1]
- [Constraint 2]
### Step 3: Add Reference Files (If Needed)
Link from SKILL.md to detailed content:
```markdown
For API reference, see [REFERENCE.md](REFERENCE.md).
For form filling guide, see [FORMS.md](FORMS.md).
Keep references one level deep from SKILL.md.
Step 4: Add Scripts (If Needed)
Scripts execute without loading into context:
## Utility Scripts
Extract fields:
```bash
python scripts/analyze.py input.pdf > fields.json
### Step 5: Test With Real Usage
1. Test with actual tasks, not test scenarios
2. Observe where Claude struggles
3. Refine based on real behavior
4. Test with Haiku, Sonnet, and Opus
## Auditing Existing Skills
Check against this rubric:
- [ ] Valid YAML frontmatter (name + description)
- [ ] Description includes trigger keywords
- [ ] Uses standard markdown headings (not XML tags)
- [ ] SKILL.md under 500 lines
- [ ] References one level deep
- [ ] Examples are concrete, not abstract
- [ ] Consistent terminology
- [ ] No time-sensitive information
- [ ] Scripts handle errors explicitly
## Common Patterns
### Template Pattern
Provide output templates for consistent results:
```markdown
## Report Template
```markdown
# [Analysis Title]
## Executive Summary
[One paragraph overview]
## Key Findings
- Finding 1
- Finding 2
## Recommendations
1. [Action item]
2. [Action item]
### Workflow Pattern
For complex multi-step tasks:
```markdown
## Migration Workflow
Copy this checklist:
- Step 1: Backup database
- Step 2: Run migration script
- Step 3: Validate output
- Step 4: Update configuration
**Step 1: Backup database**
Run: `./scripts/backup.sh`
...
Conditional Pattern
Guide through decision points:
## Choose Your Approach
**Creating new content?** Follow "Creation workflow" below.
**Editing existing?** Follow "Editing workflow" below.
Anti-Patterns to Avoid
- XML tags in body - Use markdown headings instead
- Vague descriptions - Be specific with trigger keywords
- Deep nesting - Keep references one level from SKILL.md
- Too many options - Provide a default with escape hatch
- Windows paths - Always use forward slashes
- Punting to Claude - Scripts should handle errors
- Time-sensitive info - Use "old patterns" section instead
Reference Files
For detailed guidance, see:
- official-spec.md - Anthropic's official skill specification
- best-practices.md - Skill authoring best practices
Success Criteria
A well-structured skill:
- Has valid YAML frontmatter with descriptive name and description
- Uses standard markdown headings (not XML tags)
- Keeps SKILL.md under 500 lines
- Links to reference files for detailed content
- Includes concrete examples with input/output pairs
- Has been tested with real usage
Sources:
- Agent Skills - Claude Code Docs
- Skill authoring best practices
- GitHub - anthropics/skills