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103 Early Hints: give the browser a head start

103 Early Hints is an interim response that lets a server send preload and preconnect hints before the final response is ready.

Check a URL’s status code

103 Early Hints lets a server send hints about critical resources before the real response is ready. While your application is still building the HTML, the browser can already open connections and start downloading the stylesheet, fonts or hero image the page will need.

Definition

103 comes from RFC 8297, an Experimental RFC from 2017. It is an informational response that carries Link headers, usually with rel=preload or rel=preconnect. A final response always follows, and a server may send more than one 103 first. Treat the hints as a head start only: keep the same Link headers on the final 200 so clients that ignore 103 still get them. The RFC also notes that some HTTP/1.1 clients mishandle informational responses, so servers often send 103 only over HTTP/2 or HTTP/3.

Where it helps

  • Pages with slow server “think time” (database queries, personalization, server-side rendering), where the browser would otherwise wait idle for the first byte (TTFB).
  • Critical CSS, web fonts and the image behind your Largest Contentful Paint.
  • Third-party origins you always need, such as a font host, via preconnect.

Chrome uses Early Hints for page navigations. CDNs can generate 103 for you: Cloudflare, for instance, can turn the Link headers on your responses into Early Hints. In Node.js, response.writeEarlyHints() sends one directly.

SEO impact

Early Hints is a speed feature for real visitors. It doesn’t change how a URL is indexed: crawlers act on the final status code, and Google’s status code documentation doesn’t list 103. Any benefit is indirect, through better Core Web Vitals for users. Don’t hint too much, though: preloading files the page doesn’t need wastes bandwidth and competes with the critical ones.

How to check it

Our checkers, including the HTTP header checker, report the final response, so they show the 200 and its Link headers. To see the interim 103, use curl -v or the Network panel in Chrome DevTools. Measure the effect with the page speed test.

HTTP/2 103
link: </assets/site.css>; rel=preload; as=style
link: <https://fonts.example-cdn.com>; rel=preconnect

HTTP/2 200
content-type: text/html; charset=utf-8
link: </assets/site.css>; rel=preload; as=style

Frequently asked questions

Does 103 Early Hints improve rankings?

Not directly. It can make pages load faster for visitors, which helps user experience and Core Web Vitals, but indexing is based on the final response, not the hint.

Which hints can I send in a 103 response?

Link headers with rel=preload and rel=preconnect are the ones browsers act on. Hint only resources nearly every visitor needs, such as the main stylesheet or a font host.

Why don’t I see the 103 in my status checker?

Most checkers report only the final response, usually a 200. Use curl -v or your browser’s DevTools Network panel to see interim 103 responses.