103 Early Hints (RFC 8297) lets a server send some headers, usually Link headers with rel=preload or rel=preconnect, before the final response is ready. While the server is still building the page, the browser can already open connections and download critical CSS, fonts or scripts. The final response, normally 200 OK, follows for the same request.
Browsers treat the hints as advice. Chromium-based browsers act on preload and preconnect hints in a 103 for top-level navigations over HTTP/2 and HTTP/3; other browsers support early hints to varying degrees. Clients that do not understand 103 ignore it. Some CDNs can send 103 responses for you; Cloudflare, for example, generates them from the Link headers of earlier responses.
The hints arrive before the server has decided on the final status, so the final response may still turn out to be a redirect or an error, and preloaded resources may then go unused. Headers in a 103 do not carry over to the final response; repeat them there if they matter.
Example response
HTTP/1.1 103 Early Hints
Link: </assets/app.css>; rel=preload; as=style
Link: <https://cdn.example.com>; rel=preconnect
HTTP/1.1 200 OK
Date: Fri, 06 Nov 2026 10:15:32 GMT
Content-Type: text/html; charset=utf-8
Link: </assets/app.css>; rel=preload; as=style
Link: <https://cdn.example.com>; rel=preconnect
Transfer-Encoding: chunkedSEO and redirect checking
103 has no direct SEO effect, because crawlers ignore interim responses and index the final response. Indirectly, early hints can improve loading metrics such as Largest Contentful Paint for real users. A redirect checker lists the final status of each hop; 103 responses are consumed by the HTTP client and do not appear as hops.
Common causes and use cases
- A CDN feature such as Cloudflare Early Hints replays
Link: rel=preloadheaders it saw on earlier responses. - An application server sends 103 while it queries the database or renders the page.
- The hints seem to have no effect: check that the site is served over HTTP/2 or HTTP/3 and that the hints are sent for page navigations, not for subresources.