521 Web Server Is Down
A Cloudflare-specific code: the origin actively refused the connection or is offline.
Cloudflare cannot establish a connection to the origin web server.
521 is an unofficial status code used by Cloudflare. It is not part of the HTTP standard or the IANA registry.
What HTTP 521 Web Server Is Down Means
Cloudflare cannot establish a connection to the origin web server.
A Cloudflare-specific code: the origin actively refused the connection or is offline.
Common Causes
- Origin web server is stopped or crashed
- Cloudflare IPs blocked by the origin firewall
- Origin overloaded and refusing connections
- Wrong origin IP in DNS
How to Fix It (For Visitors)
- Wait and retry
- Contact the website owner
How to Fix It (For Developers/Admins)
- Start/restart the origin web server
- Allow Cloudflare IP ranges in the firewall
- Verify the origin DNS/IP is correct
- Check server resource limits
How to Troubleshoot Cloudflare Errors
Every Cloudflare error page shows a Ray ID and tells you whether the browser, Cloudflare, or the origin host is failing. To test the origin directly while keeping the correct hostname, bypass Cloudflare with curl:
# Replace 203.0.113.10 with your origin server's IP
curl -svo /dev/null --resolve example.com:443:203.0.113.10 https://example.com/If this request fails or is slow, the problem is on the origin, not at Cloudflare. Also make sure your firewall, security plugins, and rate limiters allow Cloudflare's IP ranges.
# On the origin: is the web server listening?
sudo ss -ltnp | grep -E ':(80|443) 'Frequently Asked Questions
What does HTTP 521 Web Server Is Down mean?
A Cloudflare-specific code: the origin actively refused the connection or is offline. In short: Cloudflare cannot establish a connection to the origin web server.
Is 521 an official HTTP status code?
No. 521 is not registered in the IANA HTTP Status Code Registry; it is specific to Cloudflare. A client that receives an unrecognized status code treats it like the generic 500 code of its class.
How do I fix a 521 Web Server Is Down error?
Start/restart the origin web server. Allow Cloudflare IP ranges in the firewall. Verify the origin DNS/IP is correct.
Specification Status
521 Web Server Is Down is not an official HTTP status code. It is not registered in the IANA HTTP Status Code Registry and is specific to Cloudflare. Other servers and clients may not recognize it.