HTTP Status Codes

103 Early Hints

A performance-focused interim response that ships Link preload and preconnect hints early, letting the browser start fetching critical CSS, fonts and scripts while the server builds the page.

What it means

103 Early Hints (RFC 8297) lets a server send Link headers — usually rel=preload or rel=preconnect — before it has finished generating the final 200 response. The browser can begin fetching those resources immediately, shrinking the time the connection sits idle during server think-time. Cloudflare, Fastly and Chrome all support it.

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

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

Why it matters

  • It improves Largest Contentful Paint by starting critical-resource downloads during the server's response-generation window.
  • Unlike a redirect or a full response, it is purely additive — the final response still follows.

Common mistakes

  • Sending hints for resources the final page does not actually use, wasting bandwidth and connections.
  • Assuming universal support — older intermediaries may drop the 103, so it must be a progressive enhancement, never required for correctness.

How WebInspect checks this

  • WebInspect reports Link headers and preload/preconnect hints in the SEO and performance sections and notes HTTP-version support relevant to Early Hints.