The HTTPSave-Datarequest header is anetwork client hint which indicates the client's preference for reduced data usage.This could be for reasons such as high transfer costs, slow connection speeds, etc.

Save-Data is alow entropy hint, and hence may be sent by the client even if not requested by the server using anAccept-CH response header.Further, it should be used to reduce data sent to the client irrespective of the values of other client hints that indicate network capability, likeDownlink andRTT.

A value ofOn indicates explicit user opt-in into a reduced data usage mode on the client.When communicated to origins, this allows them to deliver alternative content to reduce the data downloaded such as smaller image and video resources, different markup and styling, disabled polling and automatic updates, and so on.

Syntax

Save-Data: <sd-token>

Directives

<sd-token>

A value indicating whether the client wants to opt in to reduced data usage mode.on indicates yes, whileoff (the default) indicates no.

Examples

UsingSave-Data: on

The following message requests a resource withSave-Data header indicating the client is opting in to reduced data mode:

GET /image.jpg HTTP/1.1Host: example.comSave-Data: on

The server responds with a200 response, and theVary header indicates thatSave-Data may have been used to create the response, and caches should be aware of this header to differentiate responses:

HTTP/1.1 200 OKContent-Length: 102832Vary: Accept-Encoding, Save-DataCache-Control: public, max-age=31536000Content-Type: image/jpeg[…]

OmittingSave-Data

In this case, the client requests the same resource without theSave-Data header:

GET /image.jpg HTTP/1.1Host: example.com

The server's response provides the full version of the content.TheVary header ensures that responses should be separately cached based on the value of theSave-Data header.This can ensure that the user is not served a lower-quality image from the cache when theSave-Data header is no longer present (e.g., after having switched from cellular to Wi-Fi).

HTTP/1.1 200 OKContent-Length: 481770Vary: Accept-Encoding, Save-DataCache-Control: public, max-age=31536000Content-Type: image/jpeg[…]

Specifications

Browser compatibility

See also

• CSS@media featureprefers-reduced-dataExperimental
• Vary header which indicates that the content served varies depending on the value ofSave-Data (seeHTTP Caching: Vary)
• NetworkInformation.saveData
• Help Your UsersSave-Data on css-tricks.com
• Delivering Fast and Light Applications with Save-Data - web.dev on web.dev
• Improving user privacy and developer experience with User-Agent Client Hints (developer.chrome.com)