Code and Claude Code hooks can conditionally tell the model anything:

#!python

print(“fix needed: method ABC needs a return type annotation on line 45”

import os

os.exit(2)

Claude Code will show that output to the model. This lets you enforce anything from TDD to a ban on window.alert() in code - deterministically.

This can be the basis for much more predictable enforcement of rules and standards in your codebase.

Once you get used to code based guardrails, you’ll see how silly the current state of the art is: why do we pack the context full of instructions, distract the model from its task, then act all surprised when it doesn’t follow them perfectly!