Hooks

Hooks are Claude Code's automation surface — deterministic bash (or any shell) scripts that fire on lifecycle events. Each hook receives JSON on stdin and returns JSON on stdout: {"decision": "approve"|"block", "reason"?: "..."}.

Events (matcher + input + output)

Every hook also receives common fields on stdin: session_id, transcript_path, cwd, permission_mode, and hook_event_name (plus agent_id/agent_type inside subagents).