hook-developer

Hooks are event handlers you register in settings.json to intercept Claude Code operations. PreToolUse and PostToolUse hooks validate or modify tool calls; other hooks like UserPromptSubmit, SessionStart, and PermissionRequest handle user input, session lifecycle, and permission flows. Register each hook with its schema and event type in your hooks configuration.

Each hook type—PreToolUse, PostToolUse, UserPromptSubmit, PermissionRequest, SessionStart, SessionEnd, Stop, SubagentStop, PreCompact, and Notification—has a defined input schema that receives event data and an output schema that returns the hook's result. Schemas standardize how hooks receive context and return decisions or modifications.

Test hooks using provided test stubs and validation patterns. Verify input schemas match event data, check output formats conform to the hook's schema, and validate lifecycle—hooks fire at correct stages and don't block critical operations. Testing patterns ensure hooks integrate safely without breaking Claude Code sessions.

Yes. PreToolUse hooks intercept tools before execution to validate, block, or modify calls. PostToolUse hooks process results after execution. PermissionRequest hooks evaluate permission checks. Together they let you enforce policies, audit tool use, and manage access control across Claude Code operations.

SessionStart and SessionEnd hooks fire at session boundaries; PreCompact hooks run before context compaction. These lifecycle hooks let you initialize state, clean up resources, and preserve context across compaction. Stop and SubagentStop hooks handle early termination in main and delegated agents.

PreToolUse intercepts tool calls before execution—use it to validate, block, or transform requests. PostToolUse runs after execution completes—use it to filter, log, or transform results. Together they bracket tool operations for comprehensive audit and control.