404 Not Found

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

When a server should send it. When nothing exists at the URL, or the server chooses not to say whether it does. Send a real 404 status with a helpful page (search, links to main sections); a "not found" page served with 200 is a soft 404. Use 410 when you know the page is gone for good.

Common causes. A typo, a deleted or moved page without a redirect, or a broken link.

What to do. Check the address. Site owners should redirect moved pages with 301 and fix internal links.

Browsers and HTTP clients. Browsers show the page the server sends; with no body, they show their own error page. Caches may store a 404 for a while, because it is cacheable by default.

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. Cacheable by default (RFC 9110 section 15.1). With no Cache-Control or Expires header, a cache may still store it and reuse it for a heuristic period, often 10% of the time since Last-Modified, so set Cache-Control explicitly if that is not what you want.

HTTP/1.1 404 Not Found
Content-Type: text/html; charset=utf-8

Not Found

location /example {
    return 404;
}

RewriteEngine On
RewriteRule ^example$ - [R=404,L]

http_response_code(404);
echo 'Not Found';
exit;

res.writeHead(404, { 'Content-Type': 'text/plain' });
res.end('Not Found');

# in a view function
return 'Not Found', 404