What it means
Cloudflare could not connect to your origin server. Server errors mean a valid request failed on the server or a service behind it.
Common causes
Origin offline, or its firewall blocking Cloudflare IP ranges.
How to fix it
Start the origin web server and allow Cloudflare IPs through the firewall.
If you are a visitor
The problem is on the website side. Wait a few minutes and reload. If it persists, check whether the site is down for everyone with the site down checker.
If you own the site
Retrying later often works. If it keeps happening, the site owner must fix the server. Short 5xx outages are usually tolerated, but errors lasting hours can make Google slow its crawling, and days of errors can drop pages from the index. A 503 with a Retry-After header is the right signal for planned downtime. Run the HTTP status checker to see exactly what your URL returns, and use uptime monitoring to be told when it changes.
अक्सर पूछे जाने वाले प्रश्न
What does HTTP 521 mean?
Web Server Is Down (Cloudflare): Cloudflare could not connect to your origin server.
Is HTTP 521 an error?
Yes. Server errors mean a valid request failed on the server or a service behind it.
Does HTTP 521 affect SEO?
Short 5xx outages are usually tolerated, but errors lasting hours can make Google slow its crawling, and days of errors can drop pages from the index. A 503 with a Retry-After header is the right signal for planned downtime.
Should I retry after HTTP 521?
Retrying later often works. If it keeps happening, the site owner must fix the server.