520 Web Server Returns Unknown Error

520

Web Server Returns Unknown Error

Example HTTP Response

HTTP Response

HTTP/1.1 520 Web Server Returns Unknown Error
Server: cloudflare
Content-Type: text/html

<html><body>Web server is returning an unknown error</body></html>

Common Causes

Origin server returned empty or malformed response
Origin sent invalid HTTP headers
Origin crashed while generating response
Origin returned a response violating HTTP protocol
PHP Fatal Error or similar backend crash
Origin's web server misconfiguration

Technical Details

What does this mean?

The server just said something completely incomprehensible! Cloudflare asked your origin server a question and got back gibberish. It's like asking for directions and getting a reply in ancient hieroglyphics.

Technical Definition

The origin web server returned an unexpected or unrecognized response to Cloudflare.

Code Snippets

Ready-to-use code for returning this HTTP status in your application:

Node.js

// Express.js
app.get('/example', (req, res) => {
  res.status(520).json({
    error: 'Web Server Returns Unknown Error',
    message: 'Your error message here'
  });
});

// Native HTTP
const http = require('http');

http.createServer((req, res) => {
  res.writeHead(520, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify({
    error: 'Web Server Returns Unknown Error',
    message: 'Your error message here'
  }));
}).listen(3000);

Related Status Codes

💥500Internal Server Error 🌉502Bad Gateway

520 Web Server Returns Unknown Error FAQ

What causes a 520 Web Server Returns Unknown Error error?

Origin server returned empty or malformed response. Origin sent invalid HTTP headers. Origin crashed while generating response. Origin returned a response violating HTTP protocol. PHP Fatal Error or similar backend crash. Origin's web server misconfiguration.

// Express.js app.get('/example', (req, res) => { res.status(520).json({ error: 'Web Server Returns Unknown Error', message: 'Your error message here' }); }); // Native HTTP const http = require('http'); http.createServer((req, res) => { res.writeHead(520, { 'Content-Type': 'application/json' }); res.end(JSON.stringify({ error: 'Web Server Returns Unknown Error', message: 'Your error message here' })); }).listen(3000);

520 Web Server Returns Unknown Error FAQ

What causes a 520 Web Server Returns Unknown Error error?