Save-Data

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

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.

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.

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) may reduce data downloads. Note that this feature is no longer supported by default in most major browser engines.

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

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:

http

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

Response:

http

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

[…]

Without `Save-Data`

Request:

http

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

Response:

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

Browser compatibility

BCD tables only load in the browser