How to Build a Claude Code Skill from Scratch

Skills enable Claude to retain expertise across sessions via slash commands, eliminating repetitive explanations of workflows and preferences. A skill is a directory containing SKILL.md file with structured instructions that activate on command, stored in ~/.claude/skills/. SKILL.md requires Trigger, Description, and Instructions sections; Examples and Constraints are optional but improve task accuracy significantly. Building a skill involves creating a directory, writing SKILL.md with clear expertise definition, and testing behavior before distribution. Skills Turn Claude Code from Assistant into Expert Claude Code is powerful out of the box. But without skills, every new session starts from zero. You explain your workflow, your preferences, your conventions - again. Skills fix that. They give Claude persistent expertise that loads on demand via slash commands. As of 2026, the Claude Code skill ecosystem is still early. Anthropic introduced the skill system in late 2025, and adoption