Status Class
5xx Server Error
Server-side failures where the request was valid but the server could not complete it.
HTTP 500 Internal Server Error: Causes and Solutions
Learn what HTTP 500 Internal Server Error means, common causes, and how to fix it. Complete troubleshooting guide for developers.
501 Not Implemented
The server doesn't support the functionality required to fulfill the request. Learn about unimplemented features.
HTTP 502 Bad Gateway: Server Communication Error
Learn what 502 Bad Gateway means, why it happens, and how to fix it. Guide covering proxy errors, upstream failures, and troubleshooting.
HTTP 503 Service Unavailable: Server Overloaded
Learn what 503 Service Unavailable means, why servers become unavailable, and how to handle temporary outages gracefully.
504 Gateway Timeout
The gateway timed out waiting for a response from an upstream server. Learn about timeout issues and solutions.
505 HTTP Version Not Supported
Learn what 505 HTTP Version Not Supported means when servers reject protocol versions. Understand HTTP/1.1, HTTP/2 compatibility and version negotiation.
507 Insufficient Storage
The server cannot store the representation needed to complete the request. Learn about storage limitations in WebDAV and file upload scenarios.
520 Web Server Returned an Unknown Error
Cloudflare-specific error when the origin server returns an unexpected response. Learn about 520 errors and how to troubleshoot them.
521 Web Server Is Down
Cloudflare-specific status code indicating the origin server refused the connection. Learn about this proxy error and how to troubleshoot it.
522 Connection Timed Out
Cloudflare-specific error when unable to establish a TCP connection to the origin server. Learn how to diagnose and fix 522 timeout errors.
523 Origin Is Unreachable
Cloudflare-specific error when the origin server's IP address is unreachable. Learn about DNS and routing issues causing 523 errors.
524 A Timeout Occurred
Cloudflare-specific error when the origin server takes too long to respond. Learn how to diagnose and fix 524 timeout errors.
Explore Other Status Classes
1xx Informational
Interim responses that indicate request progress before a final response is sent.
2xx Success
Responses indicating the request was accepted and processed successfully.
3xx Redirection
Responses that tell clients to perform additional actions, usually by following a new URL.
4xx Client Error
Client-side request issues such as invalid syntax, missing resources, or permission failures.