Save-Data

The Save-Data network client hint request header field is a boolean which indicates the client's preference for reduced data usage. This could be for reasons such as high transfer costs, slow connection speeds, etc.

Header type Request header, Client hint
Forbidden header name no
CORS-safelisted response header no

A value of On indicates explicit user opt-in into a reduced data usage mode on the client, and when communicated to origins 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) might be desirable too for reducing data downloads.

Note: The Save-Data network client hint should be used to reduce data set to the client irrespective of the values of other client client hints that indicate network capability, like Downlink and RTT.

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

The Vary header ensures that the content is cached properly (for instance ensuring that the user is not served a lower-quality image from the cache when Save-Data header is no longer present [e.g. after having switched from cellular to Wi-Fi]).

With Save-Data: on

Request:

GET /image.jpg HTTP/1.0
Host: example.com
Save-Data: on

Response:

HTTP/1.0 200 OK
Content-Length: 102832
Vary: Accept-Encoding, Save-Data
Cache-Control: public, max-age=31536000
Content-Type: image/jpeg

[...]

Without Save-Data

Request:

GET /image.jpg HTTP/1.0
Host: example.com

Response:

HTTP/1.0 200 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

Browser compatibility

BCD tables only load in the browser

See also