415 Unsupported Media Type

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

When a server should send it. When the server will not accept the body's format, as stated in Content-Type or Content-Encoding. If the problem is the encoding, add an Accept-Encoding header listing what it does accept; for the type, Accept-Post or Accept-Patch can list accepted types.

Common causes. Sending form data to an API that expects JSON, or a missing or wrong Content-Type header.

What to do. Set Content-Type to what the API expects, such as application/json.

Browsers and HTTP clients. Mostly seen in API work, for example when a request posts form data to a JSON-only endpoint or forgets the Content-Type header.

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/1.1 415 Unsupported Media Type
Accept-Post: application/json

{"status": 415, "title": "Unsupported Media Type"}

location /example {
    return 415;
}

RewriteEngine On
RewriteRule ^example$ - [R=415,L]

http_response_code(415);
echo 'Unsupported Media Type';
exit;

res.writeHead(415, { 'Content-Type': 'text/plain' });
res.end('Unsupported Media Type');

# in a view function
return 'Unsupported Media Type', 415