Early Hints

Used to return some response headers before the final response, often to preload resources.

103 Early Hints lets the server say 'start fetching these' before the real response is ready. It carries Link headers (preload, preconnect) so the browser can warm up fonts, scripts, and stylesheets while the server is still rendering the page. Chrome and Firefox both support it, and CDNs like Cloudflare can emit it automatically. The final response still arrives afterwards with its own status code.

What 103 looks like on the wire

GET / HTTP/1.1
Host: example.com

HTTP/1.1 103 Early Hints
Link: </styles/main.css>; rel=preload; as=style
Link: </scripts/app.js>; rel=preload; as=script

HTTP/1.1 200 OK
Content-Type: text/html

About 1xx Informational

The request was received and the process is continuing. These are interim responses you rarely handle directly.

Where it's defined

103 Early Hints is defined in RFC 8297 §2. MDN's 103 reference covers browser behavior and examples.