Claude Code Hooks — I/O API Reference (January 2026)

JSON schemas for hook stdin input and stdout output per event. For hook system fundamentals, activate Skill(skill: "plugin-creator:hooks-core-reference"). For working examples, activate Skill(skill: "plugin-creator:hooks-patterns").

Hook Input (JSON via stdin)

Common Fields (All Events)

{
  "session_id": "abc123",
  "transcript_path": "/path/to/session.jsonl",
  "cwd": "/current/working/directory",
  "permission_mode": "default",
  "hook_event_name": "PreToolUse"
}