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Web Architecture ReferenceIETF RFC 9110 Compliant
HTTP Status Codes Complete Reference
Standard HTTP/1.1 and HTTP/2 response codes categorized by function with SEO indexing implications.
2xx Success
200 OKStandard response for successful HTTP requests.
201 CreatedThe request succeeded and a new resource was created (POST).
204 No ContentRequest succeeded but returns no message body (e.g., DELETE).
3xx Redirection
301 Moved PermanentlyPermanent redirect; passes 100% SEO link equity to new URL.
302 Found (Temporary)Temporary redirect; search engines retain old indexing.
304 Not ModifiedClient cache is still valid; no body returned.
307 / 308 Strict RedirectsSame as 302/301 but strictly forbids changing HTTP method (POST remains POST).
4xx Client Errors
400 Bad RequestMalformed syntax, invalid JSON payload, or deceptive routing.
401 UnauthorizedAuthentication required (missing or invalid Bearer token).
403 ForbiddenAuthenticated but insufficient permission/scope to access resource.
404 Not FoundTarget endpoint does not exist on this server.
422 Unprocessable EntitySemantic validation error on request body.
429 Too Many RequestsRate limit exceeded; back off and retry later.
5xx Server Errors
500 Internal Server ErrorUncaught application exception on the backend server.
502 Bad GatewayReverse proxy (Cloudflare/Nginx) received invalid response from upstream node.
503 Service UnavailableServer overloaded or down for temporary maintenance.
504 Gateway TimeoutUpstream microservice failed to reply before proxy timeout.