The HTTP Save-Data request header is a network 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 a low entropy hint, and hence may be sent by the client even if not requested by the server using an Accept-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, like Downlink and RTT.

A value of On 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, while off (the default) indicates no.

Examples

Using Save-Data: on

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

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

The server responds with a 200 response, and the Vary header indicates that Save-Data may have been used to create the response, and caches should be aware of this header to differentiate responses:

HTTP/1.1 200 OK
Content-Length: 102832
Vary: Accept-Encoding, Save-Data
Cache-Control: public, max-age=31536000
Content-Type: image/jpeg

[…]

Omitting Save-Data

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

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

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

HTTP/1.1 200 OK
Content-Length: 481770
Vary: Accept-Encoding, Save-Data
Cache-Control: public, max-age=31536000
Content-Type: image/jpeg

[…]

Specifications

Browser compatibility

See also

• CSS @media feature prefers-reduced-data
• Vary header which indicates that the content served varies depending on the value of Save-Data (see HTTP Caching: Vary)
• NetworkInformation.saveData
• Help Your Users Save-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)