Hook Developer

This is the complete technical reference for Claude Code's hook system. If you're writing hooks, you need this. It documents all 11 hook types with exact input/output JSON schemas, explains which hooks can block execution versus just inject context, and covers registration patterns in settings.json. The critical details are here: PostToolUse uses tool_response not tool_result, Stop hooks require checking stop_hook_active to avoid infinite loops, and SessionStart can persist environment variables through CLAUDE_ENV_FILE. It's organized as a quick reference table plus detailed schemas for each hook type. Bookmark this if you're doing any serious hook development, it'll save you from guessing at field names.