14 · Shipping & Collaboration
Status Code
HTTP success and error numbers
The three-digit number in an HTTP response that says what happened: 2xx success, 3xx redirect, 4xx client problem, 5xx server problem.
Concrete example
404 means not found; 500 means the server errored; 401 means you are not authenticated.
Why it matters
The first clue when an API call or page load fails.