<objective This skill is the definitive guide for authoring Claude Code extensions. It covers four extension types: 1. Skills - Modular capabilities in SKILL.md files that provide domain expertise 2. Hooks - Event-driven automation that executes on tool use and session events 3. Slash Commands - Reusable prompts triggered with syntax 4. Subagents - Specialized Claude instances for delegated tasks All four extension types share core principles: pure XML structure, YAML frontmatter, and clear success criteria. This skill teaches you to create effective extensions following best practices. </obj…