409 Conflict

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

When a server should send it. When the request conflicts with the current state of the resource: an edit based on an old version, a duplicate unique key, a folder that already exists. Explain the conflict in the body so the client can resolve it.

Common causes. Editing a record someone else changed, creating something that already exists, or a version mismatch.

What to do. Reload the latest version, merge your change and try again.

Browsers and HTTP clients. Browsers show the body. API clients usually fetch the latest state, merge and retry, which the server cannot do for them.

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/1.1 409 Conflict
Content-Type: text/plain; charset=utf-8

Conflict

location /example {
    return 409;
}

RewriteEngine On
RewriteRule ^example$ - [R=409,L]

http_response_code(409);
echo 'Conflict';
exit;

res.writeHead(409, { 'Content-Type': 'text/plain' });
res.end('Conflict');

# in a view function
return 'Conflict', 409