HTTP 103 Early Hints
1xx Informational
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- HTTP Status Codes
- 1xx
- 103
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
Usage Example
Configure your reverse proxy or application server to emit 103 Early Hints responses containing Link headers for critical CSS, fonts, or preconnect origins. The browser begins downloading these resources immediately, reducing perceived latency while the server generates the full 200 response.
# 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;
}Related Status Codes
Common Mistakes
Mistake: Sending 103 Early Hints with cookies that conflict with the final response
Fix: Ensure that any Set-Cookie headers in the 103 response are consistent with the final response. Some proxies or servers may strip 103 headers to avoid this issue.