hook-development

Claude Code plugin hooks are event-driven automation mechanisms that trigger custom logic on specific events like PreToolUse, PostToolUse, Stop, or SessionStart. They enable developers to execute validation, automation, and context-loading tasks within plugin workflows.

You validate inputs before tool execution by implementing a PreToolUse hook that intercepts tool calls. This event-driven mechanism runs custom validation logic and security checks to ensure inputs meet your requirements before the tool executes.

Prompt-based hooks use natural language instructions for flexible task automation, while command-based hooks execute deterministic scripts for strict validation. Both handle events like PreToolUse and SessionStart but serve different automation control needs.

You load project context automatically by developing a SessionStart hook. This event-driven plugin component triggers custom logic during session initialization to load project-specific context and configure the environment before user interaction begins.

You ensure tests run before an agent stops by implementing a Stop hook in your plugin. This event-driven hook triggers custom validation logic when the Stop event fires, enforcing test execution and security checks before the session terminates.

Debugging Claude Code hooks involves using event-driven logging during PreToolUse and PostToolUse events to trace execution. Implement security best practices and validation checks to isolate failures in command-based and prompt-based hook logic.