Save-Data
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) might be desirable too for reducing data downloads.
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, whileoff
(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/1.0
Host: example.com
Save-Data: on
Response:
http
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:
http
GET /image.jpg HTTP/1.0
Host: example.com
Response:
http
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
- Help Your Users
Save-Data
- CSS Tricks - Delivering Fast and Light Applications with Save-Data - web.dev
Vary
header which indicates that the content served varies depending on the value ofSave-Data
(see HTTP Caching > Vary)- CSS @media feature
prefers-reduced-data
Experimental - Improving user privacy and developer experience with User-Agent Client Hints (web.dev)
NetworkInformation.saveData