HTTP 103 Early Hints

What is HTTP 103 Early Hints?

The 103 (Early Hints) status code is primarily used with the Link header to allow the user agent to start preloading resources while the server prepares a response. This improves perceived performance by enabling the browser to start loading critical resources — such as CSS, JavaScript, and fonts — before the final response is sent.

Common Use Cases

• Preloading critical CSS/JS before the main response
• Improving Largest Contentful Paint (LCP) performance
• Hinting preconnect to third-party origins

# Nginx configuration for 103 Early Hints
location / {
    more_set_headers -s 103 'Link: <style.css>; rel=preload; as=style';
    more_set_headers -s 103 'Link: <https://fonts.example.com>; rel=preconnect';
    proxy_pass http://backend;
}