Unofficial HTTP Status Codes
These status codes are not defined in the official HTTP specification (RFCs) but are used by popular platforms like Nginx, Cloudflare, AWS, Microsoft, and others. They are often specific to a particular service or implementation and may behave differently across systems.
499
Client Closed RequestNginx-specific: the client closed the connection before the server could respond. Common with timeouts or client-side cancellations.
520
Unknown ErrorCloudflare-specific: the origin server returned an empty, unknown, or unexpected response.
521
Web Server Is DownCloudflare-specific: the origin server refused the connection or is unreachable.
522
Connection Timed OutCloudflare-specific: the origin server took too long to respond to the connection request.
523
Origin Is UnreachableCloudflare-specific: the origin server could not be reached due to network issues.
524
A Timeout OccurredCloudflare-specific: the origin server did not send a complete response within the allowed time.
525
SSL Handshake FailedCloudflare-specific: the SSL/TLS handshake between Cloudflare and the origin server failed.
526
Invalid SSL CertificateCloudflare-specific: the origin server presented an invalid or expired SSL certificate.
527
Railgun Listener ErrorCloudflare-specific: the Railgun listener on the origin server encountered an error.
530
Origin DNS ErrorCloudflare-specific: the origin server's DNS record could not be resolved.
561
UnauthorizedAWS-specific: the request was rejected due to invalid authentication credentials (used by AWS services).
* This list includes the most common unofficial codes. Some platforms may use additional codes not listed here.