HTTP Status Codes Reference

HTTP status codes are three-digit numbers returned by servers to indicate the result of a client request. They are organized into five categories by their first digit. 1xx (Informational) codes like 100 Continue and 101 Switching Protocols indicate provisional responses during request processing. 2xx (Success) codes confirm the request was received, understood, and accepted: 200 OK is the standard success response, 201 Created confirms resource creation (typical for POST requests), 204 No Content indicates success with no response body (typical for DELETE). 3xx (Redirection) codes indicate the client must take additional action: 301 Moved Permanently for permanent URL changes (SEO-friendly), 302 Found for temporary redirects, 304 Not Modified for cache validation (browser uses cached version). 4xx (Client Error) codes indicate request problems: 400 Bad Request for malformed syntax, 401 Unauthorized for missing authentication, 403 Forbidden for insufficient permissions, 404 Not Found for non-existent resources, 429 Too Many Requests for rate limiting. 5xx (Server Error) codes indicate server-side failures: 500 Internal Server Error for unexpected conditions, 502 Bad Gateway for upstream failures, 503 Service Unavailable for temporary overload, 504 Gateway Timeout for upstream timeouts. The AllTools HTTP Status Code reference provides instant lookup with detailed explanations, common causes, and solutions for each code.

Choosing appropriate status codes for API responses is a key aspect of REST API design. Consistent status code usage makes APIs predictable and easier to consume. Common patterns include: return 200 for successful GET requests with data, 201 for successful POST that creates a resource (include Location header pointing to the new resource), 204 for successful DELETE or PUT with no response body, 400 for validation errors in the request body (include error details in the response), 401 when the request lacks valid authentication credentials, 403 when the authenticated user lacks permission for the requested action, 404 when the requested resource doesn't exist, 409 for conflict situations like duplicate entries, and 422 for semantically invalid requests (understood but cannot be processed). For error responses, include a consistent error body format: { "error": { "code": "VALIDATION_FAILED", "message": "Email is required", "details": [...] } }. Rate limiting should return 429 with Retry-After header indicating when the client can retry. The AllTools reference helps developers choose the most appropriate status code for each API endpoint response scenario, ensuring consistency across the API surface.