HTTP response codes

When you interact with an http resource, there are 5 classes of codes you are supposed to get back. It's easier to remember them if you understand how they are grouped.

100 - informational
200 - success
300 - redirect
400 - client errors
500 - server errors

The canonical 404 error code, FILE NOT FOUND, is thus a client error! You're trying to go to an unknown place, man...