Early Hints

1xx · Informational

Overview

103 Early Hints is an interim response that sends Link headers ahead of the final response so the browser can start preloading resources such as CSS, fonts, and scripts. Overlapping server processing with resource fetching improves perceived performance (for example LCP).

It carries no body, and the final response (usually 200) follows, typically repeating the same Link headers.

When it happens

Use it when the backend needs time to build the final HTML (database queries, rendering) and you want to announce critical resources during that window.
CDNs like Cloudflare and Fastly, and recent Node/Express, support it so the origin can emit the hints.

Request / Response example

Request

GET /article HTTP/1.1
Host: example.com

Response

HTTP/1.1 103 Early Hints
Link: </styles/main.css>; rel=preload; as=style
Link: </fonts/inter.woff2>; rel=preload; as=font; crossorigin

HTTP/1.1 200 OK
Content-Type: text/html
Link: </styles/main.css>; rel=preload; as=style

<!doctype html>...

In code

app.get('/article', (req, res) => {
  res.writeEarlyHints({
    link: ['</styles/main.css>; rel=preload; as=style']
  });
  renderArticle().then(html => res.send(html));
});

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

HTTP/1.1 200 OK

Notes

Modern browsers such as Chrome support 103, while clients that do not simply ignore it, so it is backward-compatible and safe to send.
For real benefit, hint only genuinely render-blocking critical resources; over-preloading wastes bandwidth.
After HTTP/2 Server Push was effectively retired, 103 Early Hints became its practical replacement.

Related status codes

200OK

Related headers

Link

Specification

RFC 8297MDN docs

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