Hooks in Claude Code

1. SPSpeaker0:00

   [upbeat music] Hooks let you run commands at different points in Claude Code's lifecycle. The key difference between hooks and everything else we covered is that hooks are deterministic. They always run. So put it this way, you can tell Claude in your claude.md file to run prettier after every file edit, and most of the time it will do that, but sometimes it won't. It's not perfect. But a hook makes it happen every single time with no exceptions. Common use cases could include auto-formatting after file edits, logging all executed commands for compliance, blocking dangerous operations like modifying production files, and sending yourself notifications when Claude finishes a task. Hooks are configured in your settings.json file. You pick an event, optionally set a matcher for which tools it applies to, and provide a command to run. User prompt submit runs when you submit a prompt before Claude processes it. Pre tool use, which runs before a tool call. Post tool use runs after a tool call completes. Notification runs when Claude sends a notification. And stop runs when Claude finishes responding. The most common hook, auto-formatting after edits. You set a post tool use hook with a matcher of edit or multi-edit, right? So it fires whenever Claude modifies a file. The command checks the file extension and runs the appropriate formatter. This could be prettier for TypeScript, go format for Go, rough for Python, whatever your project uses. Pre tool use hooks can block tool calls before they execute. So your hook receives a tool name and input as JSON on stdin. If it exits with code two, the action is blocked, and the stderr message gets fed back to Claude as feedback so Claude knows why it was blocked and can adjust. Exit code zero means proceed. Exit code two means block. This is how you enforce hard rules. Block writes to a production config directory, block batch commands that contain RM-RF, block commits to main, whatever your team needs to be guaranteed, not suggested. Hooks configured in .claude/settings.json are project level and can be checked into your repo. This means that your entire team gets the same hooks automatically. Use the Claude project dir environment variable in your commands to reference scripts stored in your project so they work regardless of Claude's current working directory. [upbeat music] Hooks gives you deterministic control over Claude Code's behavior. Use post tool use for auto-formatting and logging. Use pre tool use to block dangerous operations. Configure them in the /hooks or in settings.json, and check them into your repository so your team gets them too. If something needs to happen every time without fail, don't put it in a prompt. Put it in a hook. [upbeat music]

Episode duration: 3:21