Here is the concise list of common error codes used in public APIs, along with description.

Error code	Description
200/OK	The request was completed successfully.
201/Created	A new resource was created sucessfully.
400/Bad Request	Body of request was invalid.
401/Unauthorized Error code	The app, browser, or API call is not properly authenticated.
403/Forbidden	Caller does not have the permissions for the requested resource.
404/Not Found	Requested resource could not be found
500/Internal Server Error	Server cannot fulfill request and deos not want to expose specifics to client.
501/Not Implemented	Requested method is not currently suported.