Claude Code is useful because it can run tools, but that also means a project needs deterministic guardrails. Instructions in a prompt can be forgotten. A PreToolUse hook runs before the tool call and can reject it in code.
What we are building
This project hook inspects every Bash command. If it finds rm -rf, it writes a reason to stderr and exits with status 2. Claude Code blocks the command and receives the reason as feedback.
The important detail is the exit code:
Exit 0: the hook has no objection; normal permissions still apply.
