agent-skills

# Agent Skills

## What Are Agent Skills?

Agent Skills are modular capabilities that extend Claude's functionality by packaging instructions, metadata, and optional resources (scripts, templates) that Claude uses automatically when relevant. They transform Claude from a general-purpose assistant into a domain specialist.

## Key Benefits

- **Specialize Claude**: Tailor capabilities for specific task domains
- **Reduce repetition**: Create once, reuse across conversations automatically
- **Compose capabilities**: Combine multiple Skills for complex workflows

## How Skills Work

Skills operate within Claude's virtual machine environment with filesystem access. They use **progressive disclosure**—loading information in stages as needed rather than consuming context upfront.

### Three Loading Levels

**Level 1 - Metadata (Always loaded)**
YAML frontmatter provides discovery information (~100 tokens per Skill):
```yaml
---
name: pdf-processing
description: Extract text, fill forms, merge documents
---
```

**Level 2 - Instructions (Loaded when triggered)**
Main SKILL.md body contains procedural guidance (under 5k tokens). Claude reads this file only when the Skill matches the user's request.

**Level 3 - Resources (Loaded as needed)**
Additional files (FORMS.md, scripts, reference materials) are accessed only when referenced—effectively unlimited content without token penalty.

## Where Skills Are Available

- **Claude API**: Pre-built and custom Skills via `skill_id` parameter
- **Claude Code**: Filesystem-based custom Skills in `.claude/skills/`
- **Claude Agent SDK**: Custom Skills through configuration
- **Claude.ai**: Pre-built Skills built-in; custom Skills uploadable by users

## Pre-Built Agent Skills

Anthropic provides ready-to-use Skills:
- **PowerPoint (pptx)**: Create and edit presentations
- **Excel (xlsx)**: Build spreadsheets with data analysis
- **Word (docx)**: Generate formatted documents
- **PDF (pdf)**: Create formatted PDF reports

## Skill Stru