https://tools.ietf.org/html/rfc7231#section-6
The first digit of the status-code defines the class of response.
The last two digits do not have any categorization role. There are
five values for the first digit:
o 1xx (Informational): The request was received, continuing process
o 2xx (Successful): The request was successfully received,
understood, and accepted
o 3xx (Redirection): Further action needs to be taken in order to
complete the request
o 4xx (Client Error): The request contains bad syntax or cannot be
fulfilled
o 5xx (Server Error): The server failed to fulfill an apparently
valid request