onejob.fyi / Cloudflare error explainer
Cloudflare: Minor Service Outage · live

Error 520: the website’s server sent an answer Cloudflare couldn’t use.

or paste the whole error page
Where it broke: at the website
You your browser ✓ Cloudflare the edge in between ✓ The website the site’s own server ✕

The website’s server sent an answer Cloudflare couldn’t use. Not you.

Cloudflare reached the website, but got an empty, unknown or malformed response back. Intermittent 520s usually pass within minutes. A constant 520 needs the owner.

What to do about a 520

  1. Try again in a minutereload once, not twenty times.
  2. Try another page on the same site.
  3. Tell the site owner.Copy the report below; the Ray ID tells them exactly which request failed.

Nothing on your side causes this. VPN, cookies and browser do not matter here.

520 — if you run this site

  1. The origin crashed and dropped the connection mid-response
  2. Response headers too large (over 16 KB, often from oversized cookies)
  3. A firewall or program resetting connections from Cloudflare
  4. Invalid HTTP responses from the application

Capture the raw origin response for a failing request (tcpdump or the origin’s access log). Check header sizes and cookie bloat; check that nothing between Cloudflare and the app resets connections.

Cloudflare’s documentation