Any other event-specific fields.
Optional Readonlyhook_e.g. "PreToolUse", "PostToolUse", "Stop", "SessionStart", "PreCompact".
Optional ReadonlypromptUserPromptSubmit.
Optional ReadonlysourceSessionStart.
Optional Readonlystop_Stop / SubagentStop.
Optional Readonlytool_Optional Readonlytool_PreToolUse/PostToolUse.
Optional Readonlytool_
A hook event payload (the JSON Claude Code writes to the hook's stdin).