422 Unprocessable Content

Client error: the problem lies with the request. Repeating it unchanged will normally fail again.

When a server should send it. When the request is syntactically fine and of a type the server accepts, but the data inside fails validation: an invalid email address, a negative quantity, a missing required field. List the problems in the body, ideally per field.

Common causes. An invalid email address, a missing required field or a value outside the allowed range in an API call.

What to do. Read the error details in the response body and correct the data.

Browsers and HTTP clients. Browsers show the body. API clients and form libraries map the listed errors back to fields. Some frameworks (Rails, Laravel) use 422 by default for validation errors.

Google Search. Like every 4xx except 429, it tells Google the content does not exist: an indexed URL is removed from the index, and a new one is not processed. Crawl frequency for the URL gradually drops. Source: Google Search Central, How HTTP status codes, and network and DNS errors affect Google Search.

Caching. Not cacheable by default (RFC 9110 section 15.1 does not list it). A cache stores it only when the response says so with Cache-Control or Expires.

HTTP/1.1 422 Unprocessable Content
Content-Type: application/problem+json

{"status": 422, "title": "Unprocessable Content"}

location /example {
    return 422;
}

RewriteEngine On
RewriteRule ^example$ - [R=422,L]

http_response_code(422);
echo 'Unprocessable Content';
exit;

res.writeHead(422, { 'Content-Type': 'text/plain' });
res.end('Unprocessable Content');

# in a view function
return 'Unprocessable Content', 422