HTTP status code reference
Look up any HTTP status code, what it means, and whether a client should retry.
How it works
Codes in the 2xx range mean success, 3xx a redirect, 4xx a problem with the request and 5xx a problem on the server.
Questions
Should I retry a 500?
Only if the request is safe to repeat, and with backoff. A 503 or 429 with Retry-After is meant to be retried.
401 or 403?
401 means not signed in or bad credentials; 403 means signed in but not allowed.