Save-Data - HTTP | MDN

The HTTP Save-Data 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 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 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.

Note: Disabling HTTP/2 Server Push (RFC 7540, section 8.2: Server Push) may reduce data downloads. Note that this feature is no longer supported by default in most major browser engines.

Header type	Request header, Client hint
Forbidden request header	No
CORS-safelisted response header	No

Syntax

http

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:

http

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

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:

http

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

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

[…]

Specifications

Specification
Save Data API # save-data-request-header-field

Syntax

Directives

Examples

Using `Save-Data: on`

Omitting `Save-Data`

Specifications

Browser compatibility

See also