About 103 Early Hints
Overview of 103 Early Hints
Efficient Resource PreloadingHTTP Status Code | ||
103 Early Hints Overview 103 Early Hints is an HTTP status code that notifies clients of associated resources (e.g., CSS and JavaScript) before providing the final response. By using this code, browsers can preload relevant resources, significantly improving page load speed. |
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The server provides early information about resources related to the requested resource. |
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Resource preloading is a mechanism to preload important files (e.g., fonts, images, scripts) required by a web page. This ensures that resources are ready when needed, speeding up the page load. For instance, the browser can be instructed to “download this font beforehand” for smoother rendering. |
When is 103 Early Hints Returned?
- When the server takes time to generate the final response
- When the browser should preload related resources (e.g., CSS, JavaScript, images)
- To leverage resource preloading for improved web performance
Examples of 103 Early Hints
Early Notification of Related Resources
GET /index.html HTTP/1.1 Host: example.com
Response example:
HTTP/1.1 103 Early Hints Link: </style.css>; rel=preload; as=style Link: </script.js>; rel=preload; as=script HTTP/1.1 200 OK Content-Type: text/html; charset=UTF-8 <html> <head> <link rel="stylesheet" href="/style.css"> </head> <body> <script src="/script.js"></script> </body> </html>
Explanation: The server returns 103 Early Hints
, enabling the client to preload related resources like CSS and JavaScript. The usual 200 OK
response then provides the HTML content.
Improving Page Load Speed
GET /homepage HTTP/1.1 Host: example.com
Response example:
HTTP/1.1 103 Early Hints Link: </main.css>; rel=preload; as=style Link: </analytics.js>; rel=preload; as=script HTTP/1.1 200 OK Content-Type: text/html; charset=UTF-8 [HTML content of the homepage]
Explanation: By using 103 Early Hints
, the browser can download required resources in advance, enhancing page load speed.
Points to Consider
Key points when returning 103 Early Hints:
- Ensure the Final Response is Accurate
103 Early Hints
is a supplementary status code, and the final response (e.g.,200 OK
) must be correctly provided. - Check Client Support
Not all browsers or clients support103 Early Hints
, so compatibility should be considered.
Comparison with Related HTTP Status Codes
An explanation of status codes related to 103 Early Hints:
- 200 OK: Used when a request is successful and a complete response is provided.
- 102 Processing: Indicates that a long process is ongoing, serving a different purpose than 103.
Understanding these differences helps in appropriately using the 103 status code.