It's interesting that this law is the exact opposite of the Robustness Principle / Postel's Law.

> be conservative in what you send, be liberal in what you accept

If you are liberal in what you accept, you'd better understand the ways in which you've been liberal, and document them (at least) internally, because you're going to have to support all those ways forever, even after huge codebase changes, due to Hyrum's Law.

I try to avoid creating APIs which are "liberal in what they accept" for exactly that reason.

> I try to avoid creating APIs which are "liberal in what they accept" for exactly that reason.

That's my preference too. When you have relaxed criteria about what kind of data you accept via an API I find you inevitably end up having to make decisions about how to massage that data in to some sort of canonical format, and those decisions almost always seem to end up leading to behaviour that's surprising to users in one way or another.