Description

The HTTP response status code 520 Web Server Returned an Unknown Error is an unofficial HTTP status code specific to Cloudflare.

The 520 error occurs when the origin web server returns an empty, unknown, or unexpected response to Cloudflare. This is often a catch-all error for situations where the origin server returns something that Cloudflare cannot interpret.

Common causes include:

• The origin server crashing or restarting mid-request.
• The origin server returning a response that violates HTTP specifications.
• Firewall or security software on the origin blocking Cloudflare's request.

See Also

• Cloudflare docs