520
Web Server Returns Unknown Error
A Cloudflare-specific status code meaning the origin server returned an empty, unknown, or unexpected response that Cloudflare could not process. This is not a standard HTTP status code — it exists only in the Cloudflare ecosystem.
What does HTTP 520 mean?
A Cloudflare-specific status code meaning the origin server returned an empty, unknown, or unexpected response that Cloudflare could not process. This is not a standard HTTP status code — it exists only in the Cloudflare ecosystem.
Common causes
- 1
The origin server returned an empty response (no headers, no body) or closed the connection before sending anything.
- 2
The origin server returned response headers that exceed Cloudflare's 32KB header size limit, or the headers are malformed.
- 3
The origin server crashed mid-response, returning a partial or corrupted HTTP response that Cloudflare cannot parse.
How to fix it
- 1
Check origin server logs for errors. A 520 is Cloudflare telling you something is wrong on your server — the real error is in your server logs, not Cloudflare's.
- 2
Reduce response header size. Remove excessively large cookies, debug headers, or unnecessary custom headers that push total header size over 32KB.
- 3
Ensure your origin server completes responses properly. If the server process is crashing, check for out-of-memory errors or unhandled exceptions.
Monitor for HTTP 520 errors
If you use Cloudflare, a 520 indicates your origin server is misbehaving. Uptrack detects these Cloudflare-specific errors and alerts you, even though they are not standard HTTP codes.
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