Hooks

Hooks are commands that Claude Code runs automatically at defined points in the lifecycle — before using a tool, after editing a file, when you submit a prompt, when a session starts. The difference from an instruction in CLAUDE.md is the guarantee: CLAUDE.md asks the model for something, and it may forget or ignore it; a hook is your own code that always runs. It's Claude Code's deterministic mechanism.

#Events

Each hook attaches to an event. Among the available ones:

• PreToolUse — before Claude runs a tool (can block execution).
• PostToolUse — after a tool runs successfully.
• UserPromptSubmit — when you submit a prompt, before Claude processes it.
• SessionStart / SessionEnd — at the start and end of a session.
• Stop — when Claude finishes responding.
• SubagentStop — when a subagent completes.
• Notification — when Claude Code emits a notification (for example, asking for permission).
• PreCompact — before compacting the context window.