501 Not Implemented

What HTTP 501 Not Implemented Means

The server does not support the functionality required to fulfill the request.

Server doesn't recognize the request method or can't fulfill it.

Common Causes

• HTTP method not implemented
• Feature not supported
• Unrecognized request method

How to Fix It (For Visitors)

• Contact website administrator
• Use different client/browser

How to Fix It (For Developers/Admins)

• Implement the requested method
• Return 405 if method not allowed
• Update server software
• Enable required modules

Returning a 501 Not Implemented (Code Examples)

If you build APIs or web apps, here is how to send an HTTP 501 response and how to test for it:

Node.js (Express)

app.get('/resource', (req, res) => {
  res.status(501).json({ error: 'Not Implemented' });
});

Python (Flask)

@app.route('/resource')
def resource():
    return jsonify(error='Not Implemented'), 501

PHP

<?php
http_response_code(501);
header('Content-Type: application/json');
echo json_encode(['error' => 'Not Implemented']);

Check the status with curl

curl -I https://example.com/resource
# Look for: HTTP/1.1 501 Not Implemented

Frequently Asked Questions

What does HTTP 501 Not Implemented mean?

Server doesn't recognize the request method or can't fulfill it. In short: The server does not support the functionality required to fulfill the request.

Is a 501 Not Implemented error my fault or the website's?

501 is a 5xx server-error code, so the problem is on the server side, not your browser or device. As a visitor you can usually only retry; if you run the site, investigate the server.

How do I fix a 501 Not Implemented error?

Implement the requested method. Return 405 if method not allowed. Update server software.

Official Specification

The 501 Not Implemented status code is defined in RFC 7231 Section 6.6.2.

View the IANA HTTP Status Code Registry →