HTTP 521 Web Server Is Down

The origin web server has refused or is not responding to Cloudflare's connection.

What 521 means

HTTP 521 is a Cloudflare-specific error code indicating that the origin web server refused the connection from Cloudflare. This means Cloudflare can't reach your server at all.

Common causes

• Origin server is completely down
• Origin firewall blocking Cloudflare IPs
• Origin server crashed
• Port not open on origin server

How to fix it

• Check if your origin server is running
• Whitelist Cloudflare IP ranges in your firewall
• Verify the correct origin IP in Cloudflare settings
• Check that your web server is listening on the correct port

SEO impact

Critical. Your entire site is unreachable through Cloudflare. Search engines will see an error page.

Monitoring tip

LemWatch monitors through CDN layers like Cloudflare and can distinguish between CDN errors and origin server issues.