ContextQMD
Back to Content

Sec-CH-DPR header

files/en-us/web/http/reference/headers/sec-ch-dpr/index.md

latest2.3 KB
Original Source

{{SecureContext_Header}}{{SeeCompatTable}}

The HTTP Sec-CH-DPR {{Glossary("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 {{Glossary("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 `` srcset attribute to allow user agents to select a preferred image.

If the Sec-CH-DPR header appears more than once in a message the last occurrence is used.

Servers that opt in to the Sec-CH-DPR client hint will typically also specify it in the {{HTTPHeader("Vary")}} header to inform caches that the server may send different responses based on the header value in a request.

<table class="properties"> <tbody> <tr> <th scope="row">Header type</th> <td> {{Glossary("Request header")}}, <a href="/en-US/docs/Web/HTTP/Guides/Client_hints">Client hint</a> </td> </tr> <tr> <th scope="row">{{Glossary("Forbidden request header")}}</th> <td>No</td> </tr> </tbody> </table>

Syntax

http
Sec-CH-DPR: <number>

Directives

  • <number>
    • : The client device pixel ratio.

Examples

A server must first opt in to receive the Sec-CH-DPR header by sending the response header {{HTTPHeader("Accept-CH")}} containing the directive Sec-CH-DPR.

http
Accept-CH: Sec-CH-DPR

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

http
Sec-CH-DPR: 2.0

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also