HTTP Status Codes

Use the right HTTP status code for the failure, return a consistent body with a stable error code, a human message, and a trace id, never leak stack traces, and centralise mapping with @RestControllerAdvice.

The class digit tells you who is at fault and the exact code tells you precisely why: 400 vs 422, 301 vs 308, 502 vs 503 vs 504, 401 vs 403, and 429 vs 503 each carry a distinct instruction for the client.

HTTP status codes are three-digit numbers that summarise the outcome: 2xx means success, 3xx means redirect, 4xx means the client made a mistake, and 5xx means the server failed.

401 means not authenticated, so log in; 403 means authenticated but not permitted, so logging in again will not help.