Is an HTTP 503 error always a server-side problem, or can client-side issues cause it?

An HTTP 503 error is fundamentally a server-side problem. The server itself is reporting that it cannot fulfill the request due to temporary unavailability. It's not caused by client-side issues like browser settings, corrupted cached data, or user network problems. While a client's request *might* contribute to server overload, the 503 response unequivocally originates from the server acknowledging its temporary incapacity.