craft-hooklisted

# Skill: Craft Hook > "The Subconscious. Automatic reactions." ## 0. Read The Docs First https://code.claude.com/docs/en/hooks is the source of truth. This skill is what we learned around it, and Anthropic adds events without asking us. ## 1. The Principles - **Thin**: Hooks point to skills. They don't contain protocols. - **Invisible**: A good hook is never noticed. It just *works*. - **Non-Blocking**: Hooks complete quickly. Long tasks belong in agents. - **Focused**: One hook, one job. Use matchers to target precisely. - **Verified**: Test that Claude actually sees your output. ### The Thin Hook Rule If you're writing more than 5 lines of protocol/criteria in a hook, it belongs in a skill. ``` HOOK RESPONSIBILITY SKILL RESPONSIBILITY ├── WHEN to inject ├── HOW to do it ├── WHAT to tell Claude ├── WHY to do it ├── Formatting (emojis) └── Decision criteria └── Exit code / JSON output ``` **Anti-pattern**: Duplicating skill content in hooks. ## 2. Context Injection Rules **Critical**: Not all hooks can inject to Claude's context. Know the rules: | Event | stdout (exit 0) | stderr (exit 2) | JSON additionalContext | |-------|-----------------|-----------------|------------------------| | `SessionStart` | **→ Claude** | → User only | **→ Claude** | | `UserPromptSubmit` | **→ Claude** | → User only | **→ Claude** | | `Setup` | **→ Claude** | → User only | **→ Claude** | | `PreToolUse` | → User verbose | **→ Claude** | **→