DPR

Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.

Non-standard: This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

Warning: The DPR header was removed from the client hints specification in draft-ietf-httpbis-client-hints-07. The proposed replacement is Sec-CH-DPR (Responsive Image Client Hints).

The HTTP DPR request header provides device client hints about the client device pixel ratio (DPR). This ratio is the number of physical device pixels corresponding to every CSS pixel.

The hint is useful when selecting image sources that best correspond to a screen's pixel density. This is similar to the role played by x descriptors in the <img> srcset attribute to allow user agents to select a preferred image.

If a server uses the DPR hint to choose which resource is sent in a response, the response must include the Content-DPR header. The client must use the value in Content-DPR for layout if it differs from the value in the request's DPR header. If the DPR header appears more than once in a message the last occurrence is used.

Servers that opt in to the DPR client hint will typically also specify it in the Vary header to inform caches that the server may send different responses based on the header value in a request.

Header type Request header, Client hint
Forbidden header name No

Syntax

http
DPR: <number>

Directives

<number>

The client device pixel ratio.

Examples

A server must first opt in to receive the DPR header by sending the response header Accept-CH containing the directive DPR.

http
Accept-CH: DPR

Then on subsequent requests the client might send DPR header to the server:

http
DPR: 2.0

If a request with the DPR header (as shown above) is for an image resource, then the server response must include the Content-DPR header:

http
Content-DPR: 2.0

Browser compatibility

BCD tables only load in the browser

See also