Glossary: System Design Basics in C#

Status codes

Also written: Status code, HTTP status code, 200, 201, 400, 401, 403, 404, 409, 429, 500, 503

The number that starts an HTTP response: 2xx means success, 4xx the client's mistake, 5xx the server's problem. Common ones are 200 OK (found), 201 Created (order placed), 400 Bad Request (invalid input), 401 Unauthorized (not logged in), 403 Forbidden (known but not allowed), 404 Not Found (unknown SKU), 409 Conflict (clashes with current state), 429 Too Many Requests (hammering the API), 500 Internal Server Error (a bug) and 503 Service Unavailable (try later); 301 and 302 are redirects.