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The Sec-CH-Prefers-Reduced-Motion HTTP Header is an internal header that allows the user agent to hint to the server about the client's user preference concerning motion. It is a part of client hints, which are a set of request headers where the client hints to the server about certain information, like device characteristics, that should influence the server's response. It aids in improving user experience by delivering optimized or personalized content, particularly helpful for those with motion sensitivity as certain animations could trigger such sensitivities.
Value - This can be set to "reduce" to indicate that the client has requested reduced motion, or "no-preference" which means the user has no particular preference towards reduced motion.
GET /example HTTP/2 Host: example.com Sec-CH-Prefers-Reduced-Motion: reduce
This request will hint the server that the client prefers reduced motion.
How to modify Sec-CH-Prefers-Reduced-Motion HTTP
ModHeader is a Google Chrome extension that allows you to modify and manipulate HTTP request headers. You can use this extension to modify the Sec-CH-Prefers-Reduced-Motion header. To do this, install the ModHeader extension on your Chrome browser. First, open the extension settings by clicking its icon on the toolbar. Click on "Request headers", then "+ add". On the left, fill in "Sec-CH-Prefers-Reduced-Motion", and on the right, select either "reduce" or "no-preference". This can be useful for testing server responses to different client motion preferences, or if you want to experience reduced motion on websites that support the header.