How to Write Effective Agent Skills for Claude

If you use Claude Code or claude.ai, you've probably caught yourself giving the same instructions over and over. "Use conventional commits." "Run the linter before committing." "Check for breaking changes." Every new conversation, you start from scratch. Agent Skills fix this. You package your instructions, conventions, and scripts into a reusable module that Claude picks up automatically. What are Agent Skills? Skills are directories containing a SKILL.md file with instructions, optional reference files, and optional scripts. Think of them as onboarding docs for Claude — reusable and automatically triggered when your request matches. Anthropic ships pre-built Skills (PowerPoint, Excel, Word, PDF). The real power is custom Skills: your expertise, your conventions, your patterns. Where they work: Claude Code — drop into .claude/skills/ (project) or ~/.claude/skills/ (global). Auto-discovered. claude.ai — upload as zip via Settings > Features (Pro/Max/Team/Enterprise). Skills don't sy