200 - Generic everything is OK
201 - Created something OK
202 - Accepted but is being processed async (video is encoding, image is resizing, etc)
400 - Wrong arguments (missing validation)
401 - Unauthorized (no current user and there should be)
403 - The current user is forbidden from accessing this data
404 - That URL is not a valid route, or the item resource does not exist
410 - Data has been deleted, deactivated, suspended, etc
405 - Method Not Allowed (your framework will probably do this for you)
500 - Something unexpected happened and it is the APIs fault
503 - API is not here right now, please try again later