Cloudflare 520: Web server returned an unknown error

Meaning

This happens due to issues between Cloudflare and the origin server.

Causes

• Origin server is unreachable or slow.
• TLS/SSL issues between Cloudflare and origin.

How to fix

• Check origin server health and firewall rules.
• Verify SSL/TLS configuration and certificates.

Example

Cloudflare 520

Official references

Cloudflare status codes (52x)ReferenceDocshttps://developers.cloudflare.com/analytics/account-and-zone-analytics/status-codes/Open in new tab Cloudflare 5xx troubleshootingSupportSupporthttps://developers.cloudflare.com/support/troubleshooting/cloudflare-errors/troubleshooting-cloudflare-5xx-errors/Open in new tab Cloudflare error troubleshooting indexSupportSupporthttps://developers.cloudflare.com/support/troubleshooting/cloudflare-errors/Open in new tab Cloudflare 520 troubleshootingSupportSupporthttps://developers.cloudflare.com/support/troubleshooting/cloudflare-errors/Open in new tab

FAQ

• Is it on my side? — Usually it’s a server/network issue.
• Will retrying help? — If temporary, a retry may succeed.

When to contact support

Contact the site owner to check origin health.