[Izkata]

I think the idea behind 418, as much as there was an idea beyond a joke, was to indicate you sent your request to a teapot instead of a server. So yeah, client error for why it's not 518 instead.

But it works in this example for "client did something weird I don't understand", so still client error - something akin to a 404, "client tried to go somewhere I don't understand".

[OJFord]

Yes, exactly, I wasn't excluding 418 in saying all 4xx are errors in the client's request.

But 'client did something weird I don't understand' is a 400, 405, something; not the same as 'this cannot happen' at all.

[mekkkkkk]

But it's the clients fault for trying to communicate with a teapot. There's nothing wrong inside the teapot. You just tried to communicate with a teapot. That's silly. Here's a 418 for you.

[OJFord]

Again, yes, I am not saying 418 is wrong to be 4xx, I am including it in 'the entire 4xx range are client errors'.