Using Claude Code PreToolUse Hooks to Block Invalid Commands
July 29, 2026
Claude Code allows attaching shell scripts to lifecycle events, specifically the PreToolUse hook. By intercepting tool calls as JSON, users can block specific commands—such as using npm in a pnpm repository—and pass rejection reasons back into the model context.
HOW THIS AFFECTS YOU
●
builderYou can implement programmatic guardrails to prevent AI agents from executing incorrect or unauthorized terminal commands.