hooks-designer

Write a PreToolUse hook script matching the Bash tool that inspects tool_input.command for git commit, checks a condition such as a test-passed marker file, and exits with code 2 plus a stderr message to block. Register it in .claude/settings.json under hooks.PreToolUse.

PreToolUse hooks fire before a tool executes and can block it with exit code 2, while PostToolUse hooks fire after execution and are used for logging, validation, or follow-up actions like auto-formatting written files.

Exit code 0 allows the tool to proceed, exit code 1 signals a hook error and fails open so the tool still runs, and exit code 2 blocks execution with the stderr message shown to Claude as the reason.

Common causes are a missing chmod +x on the script, a matcher that does not match the tool name, or jq parsing failures on the stdin JSON. Test the hook directly by piping sample JSON into it and checking the exit code.

Avoid hooks for CI/CD pipelines running Claude headlessly, for extending Claude with new tools (use MCP servers instead), and for blocking mid-task file writes, which confuses the agent. Gate at natural checkpoints like commit or push instead.