Downlink header

Limited availability

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

Experimental:This is anexperimental technology
Check theBrowser compatibility table carefully before using this in production.

The HTTPDownlinkrequest header is used inClient Hints to provide the approximate bandwidth in Mbps of the client's connection to the server.

The hint allows a server to choose what information is sent based on the network bandwidth.For example, a server might choose to send smaller versions of images and other resources on low bandwidth networks.

Note:TheVary header is used in responses to indicate that a different resource is sent for every different value of the header (seeHTTP Caching Vary).Even ifDownlink is used to configure what resources are sent, consider omitting it in theVary header — it is likely to change often, which effectively makes the resource uncacheable.

Header type	Request header,Client hint
Forbidden request header	No

Syntax

http

Downlink: <number>

Directives

<number>: The downlink rate in Mbps, rounded to the nearest 25 kilobits.The downlink rate may be used as afingerprinting variable, so values for the header are intentionally coarse to reduce the potential for its misuse.