5xx Server error Non-standard · used by Cloudflare
HTTP 520 Web Server Returned an Unknown Error
A Cloudflare code: the origin server answered Cloudflare with something empty, unknown or unexpected, so Cloudflare couldn’t pass on a valid response. It is a catch-all for origin responses Cloudflare can’t use.
Documented in Cloudflare: 5xx errors(opens in a new tab)
//_01 Uptime checks
Is 520 up or down for a monitor?
Uptimecheck HTTP monitor
Default settings
Down. It is outside the default 200–399 range, so a monitor reports an outage once a second check confirms it. If 520 is the answer you expect from that URL, add it to the monitor’s expected status codes.
Is it down? checker
Free, at /is-it-down/
Down. A 5xx means the server, or something in front of it, failed to answer.
//_02 Causes and fixes
Why you see 520 and what to do
Typical causes
- The origin crashed or reset the connection while answering.
- Response headers larger than Cloudflare accepts, or an empty response.
If you run the site
- Read the origin’s error logs at the time of the error, and test the origin directly without Cloudflare.
If you’re a visitor
- Reload in a minute; the problem is on the site’s server.
Know the moment your site stops answering as it should
An Uptimecheck monitor requests your page as often as every minute, checks the status code against the ones you expect, confirms a failure with a second check and then alerts you.
14-day free trial · No credit card required
Questions
What does HTTP 520 mean?
A Cloudflare code: the origin server answered Cloudflare with something empty, unknown or unexpected, so Cloudflare couldn’t pass on a valid response. It is a catch-all for origin responses Cloudflare can’t use.
Does an uptime monitor count 520 as down?
Down. It is outside the default 200–399 range, so a monitor reports an outage once a second check confirms it. If 520 is the answer you expect from that URL, add it to the monitor’s expected status codes.
Downtime is obsolete.
Set up your first monitor in under a minute, or look around the live demo first.
14-day free trial · No credit card required