Apply Hyrum's Law when discussing API design, backward compatibility, deprecation, versioning, or any situation where a system has enough users that its observable behavior—not just its documented interface—has become depended upon. Trigger on phrases like "can we change this behavior?", "is this a breaking change?", "users are depending on a bug we fixed", "we want to deprecate this", or any discussion about evolving a public or widely-used API. Hyrum's Law is essential reading for anyone building platforms, libraries, or APIs.
