103 Early Hints HTTP Status Code

Description

The HTTP status code 103 is called Early Hints. It's an informational response that a server can send to a browser before it sends the final response to a request.

The purpose of this code is to give the browser some advance information about the final response. This can help the browser to improve the loading speed of the webpage.

Specifically, the 103 Early Hints code is often used with a header called Link. The Link header tells the browser about resources that it will need to load in order to display the webpage. By receiving this information early, the browser can start preloading these resources in the background, while the server is still working on the final response. This can make the webpage appear to load faster for the user.

Here are some key points about the 103 Early Hints code:

It is only intended to be used with HTTP/2 protocol. Using it with HTTP/1.1 can cause compatibility issues.
The server is not guaranteed to include all of the headers from the 103 response in the final response.
Browsers that do not understand the 103 code will simply ignore it and wait for the final response.

Overall, the 103 Early Hints code is a relatively new feature that can help to improve the performance of web pages. However, it is not yet universally supported by all browsers and servers.

Status

HTTP

103 Early Hints

Common Causes

Here are some of the main reasons and contexts in which a 103 status code might be used:

Link Rel Preload: This status code is often used in conjunction with the Link header to allow a server to start sending resources that a client will need to render the page, such as stylesheets, scripts, and images, before the server has finished processing the entire request. This can help improve the performance of web applications by allowing the browser to start fetching these resources early.
Performance Optimization: The primary motivation behind the 103 Early Hints response is to optimize the loading performance of web pages. By providing hints about which resources will be needed, the server can instruct the client to begin fetching these resources in parallel with the server's processing, potentially reducing the overall time to render the page to the user.
Server Still Processing: The server sends a 103 response to indicate that it has received the request and is processing it, but has not yet completed the request. This can be particularly useful for requests that take a long time to process, providing an intermediate response to keep the connection alive and inform the client that the request is being handled.
Use in HTTP/2 and HTTP/3: While particularly useful in HTTP/2 and HTTP/3 environments where multiple resources can be loaded in parallel more efficiently, the 103 status code can be used in any HTTP protocol version to improve loading times and enhance the user experience.

It's important to note that the 103 Early Hints response is a relatively recent addition to the HTTP status codes and may not be universally supported by all web servers or clients. However, its adoption can provide performance benefits in scenarios where early loading of web resources is beneficial.