5xx Status Codes
5xx server errors
Section titled “5xx server errors”500 Internal Server Error
Section titled “500 Internal Server Error”A generic error message indicating that an unexpected condition was encountered, and no specific message is available.
501 Not Implemented
Section titled “501 Not Implemented”The server does not recognize the request method or lacks the ability to fulfill the request, typically implying future availability.
502 Bad Gateway
Section titled “502 Bad Gateway”The server, acting as a gateway or proxy, received an invalid response from the upstream server.
503 Service Unavailable
Section titled “503 Service Unavailable”The server cannot handle the request due to being overloaded or down for maintenance. This is usually a temporary state.
504 Gateway Timeout
Section titled “504 Gateway Timeout”The server, acting as a gateway or proxy, did not receive a timely response from the upstream server.
505 HTTP Version Not Supported
Section titled “505 HTTP Version Not Supported”The server does not support the HTTP version used in the request.
506 Variant Also Negotiates (RFC 2295)
Section titled “506 Variant Also Negotiates (RFC 2295)”Transparent content negotiation resulted in a circular reference.
507 Insufficient Storage (WebDAV; RFC 4918)
Section titled “507 Insufficient Storage (WebDAV; RFC 4918)”The server is unable to store the representation needed to complete the request.
508 Loop Detected (WebDAV; RFC 5842)
Section titled “508 Loop Detected (WebDAV; RFC 5842)”The server detected an infinite loop while processing the request, indicating a problem with the request processing.
510 Not Extended (RFC 2774)
Section titled “510 Not Extended (RFC 2774)”Further extensions to the request are required for the server to fulfill it.
511 Network Authentication Required (RFC 6585)
Section titled “511 Network Authentication Required (RFC 6585)”The client needs to authenticate to gain network access, often used by intercepting proxies to control network access.
Unofficial codes
Section titled “Unofficial codes”509 Bandwidth Limit Exceeded (Apache Web Server/cPanel)
Section titled “509 Bandwidth Limit Exceeded (Apache Web Server/cPanel)”The server has exceeded the bandwidth limit set by the administrator, commonly used by shared hosting providers.
529 Site is Overloaded
Section titled “529 Site is Overloaded”Indicates that the site cannot process the request, as used by Qualys in the SSLLabs server testing API.
530 Site is Frozen
Section titled “530 Site is Frozen”Used by Pantheon Systems to indicate a site that has been frozen due to inactivity.
530 Origin DNS Error (Shopify)
Section titled “530 Origin DNS Error (Shopify)”Indicates that Cloudflare cannot resolve the requested DNS record, as used by Shopify.
540 Temporarily Disabled (Shopify)
Section titled “540 Temporarily Disabled (Shopify)”Used by Shopify to signal that the requested endpoint has been temporarily disabled.
598 Network Read Timeout Error
Section titled “598 Network Read Timeout Error”An informal error used by some HTTP proxies to signal a network read timeout behind the proxy.
599 Network Connect Timeout Error
Section titled “599 Network Connect Timeout Error”An error used by some HTTP proxies to indicate a network connect timeout behind the proxy.
Cloudflare
Section titled “Cloudflare”520 Web Server Returned an Unknown Error
Section titled “520 Web Server Returned an Unknown Error”The origin server returned an empty, unknown, or unexpected response to Cloudflare.
521 Web Server Is Down
Section titled “521 Web Server Is Down”The origin server refused connections from Cloudflare, possibly due to security measures blocking legitimate connections.
522 Connection Timed Out
Section titled “522 Connection Timed Out”Cloudflare timed out while trying to contact the origin server.
523 Origin Is Unreachable
Section titled “523 Origin Is Unreachable”Cloudflare could not reach the origin server, often due to incorrect or missing DNS records.
524 A Timeout Occurred
Section titled “524 A Timeout Occurred”Cloudflare successfully connected to the origin server but did not receive a timely HTTP response.
525 SSL Handshake Failed
Section titled “525 SSL Handshake Failed”Cloudflare could not negotiate an SSL/TLS handshake with the origin server.
526 Invalid SSL Certificate
Section titled “526 Invalid SSL Certificate”Cloudflare could not validate the SSL certificate on the origin web server. This is also used by Cloud Foundry’s gorouter.
527 Railgun Error (obsolete)
Section titled “527 Railgun Error (obsolete)”Previously indicated an interrupted connection between Cloudflare and the origin server’s Railgun server; this error is now obsolete.
AWS Elastic Load Balancing (ELB)
Section titled “AWS Elastic Load Balancing (ELB)”561 Unauthorized
Section titled “561 Unauthorized”An authentication error returned by a server registered with a load balancer. This occurs when a listener rule is set to authenticate users, but the identity provider (IdP) encounters an error during the authentication process.