Code 520

This is a catch-all response for when a website behind Cloudflare returns something unexpected or something that is not tolerated/interpreted (protocol violation or empty response).

While the 520 error can be triggered by very unique and strange edge-case scenarios, they are generally caused by:

• Connection resets (following a successful TCP handshake)
• Headers exceed the Cloudflare header size limit (over 8kb)
• An empty response from origin
• An invalid HTTP response
• Missing response headers from an HTTP response
• Presence of multiple Content-Length headers