HTTP 103 Early Hints
Used to return some response headers before the final HTTP message.
1xx Informational
103
Early Hints
Description
The 103 Early Hints informational status code indicates to the client that the server is likely to send a final response with the header fields included in the informational response. A server can send multiple 103 responses before the final response. This is primarily used to allow the user agent to speculatively preload resources that are likely to be used in the final response, such as stylesheets, scripts, or fonts, improving page load times. The server uses Link headers in the 103 response to indicate which resources the client should begin loading early. The client can then start fetching these resources while the server is still processing the main response.
When Is It Used?
Used by servers to improve web performance by hinting to browsers which resources to preload. For example, a server can send Link headers for CSS and JS files while the backend is still generating the full HTML response, allowing browsers to start downloading these assets earlier.
Example Response
HTTP/1.1 103 Early Hints
Link: </styles.css>; rel=preload; as=style
Link: </script.js>; rel=preload; as=script