How to Build Claude Code Custom Skills for Automated Code Review

What Are Claude Code Custom Skills? Claude Code supports custom skills — reusable command sets you define once and invoke with /command-name . They live in .claude/skills/ and are loaded automatically. .claude/ └── skills/ ├── code-review/ │ └── SKILL.md ← /code-review logic goes here └── secret-scanner/ └── SKILL.md ← /secret-scanner logic goes here Instead of typing the same 20-line prompt every time you want a code review, you write it once in SKILL.md and run /code-review src/api/ forever after. Building a Code Review Skill from Scratch SKILL.md Structure # skill-name — one-line description ## Overview What this skill does ## Trigger Conditions When to call this skill ## Steps 1. Step 1 2. Step 2 ## Output Format What the output looks like Example: /code-review Skill Here's a complete 5-axis code review skill (design, readability, performance, security, testability): .claude/skills/code-review/SKILL.md : # code-review — 5-Axis Code Review Skill ## Overview Review code across 5 axes