Guide for creating effective, portable skills that extend Claude's capabilities with specialized knowledge, workflows, and tool integrations. Use when: (1) Creating a new skill from scratch, (2) Updating or improving an existing skill, (3) Structuring skill content for progressive disclosure, (4) Writing skill descriptions and triggers, (5) Packaging a skill for distribution. Triggers on: "create a skill", "build a skill", "new skill", "update this skill", "improve skill description", "skill structure", "skill triggers".