HTTP 421 Misdirected Request

What does HTTP 421 mean?

The request was sent to a server that cannot answer for that host name. Seen with HTTP/2 connection reuse: the browser reuses a connection for another domain covered by the same TLS certificate, but the server is not configured for that domain.

4xx Client error: The request has a problem the client can fix: wrong URL, missing credentials, bad data or too many requests.

How to fix 421 Misdirected Request

• Make sure every host name on a shared certificate is configured on the server, or use separate certificates.

421 and SEO

Can block crawling of affected host names until fixed.

Example response

HTTP/1.1 421 Misdirected Request

How to return a 421 response

Node.js (Express)

res.status(421).json({ error: 'Misdirected Request' });

PHP

http_response_code(421);

Python (Flask)

return {'error': 'Misdirected Request'}, 421

Go (net/http)

w.WriteHeader(421)

nginx

return 421;

Related status codes

• 400 Bad Request — The server cannot process the request because it is malformed.
• 502 Bad Gateway — A gateway or proxy got an invalid response from the upstream server.

Check which status code a URL returns with the HTTP header checker.