Sec-CH-Viewport-Width header
Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.
The HTTP Sec-CH-Viewport-Width request header is a device client hint which provides the client's layout viewport width in CSS pixels.
The value is rounded up to the smallest following integer (i.e., ceiling value).
The hint can be used with other screen-specific hints to deliver images optimized for a specific screen size, or to omit resources that are not needed for a particular screen width.
If the Sec-CH-Viewport-Width header appears more than once in a message the last occurrence is used.
A server has to opt-in to receive the Sec-CH-Viewport-Width header from the client, by sending the Accept-CH response header.
Servers that opt-in will typically also specify it in the Vary header which informs caches that the server may send different responses based on the header value in a request.
| Header type | Request header, Client hint |
|---|---|
| Forbidden request header | No |
Syntax
Sec-CH-Viewport-Width: <number>
Directives
<number>-
The width of the user's viewport in CSS pixels, rounded up to the nearest integer.
Examples
Using Sec-CH-Viewport-Width
A server must first opt-in to receive the Sec-CH-Viewport-Width header by sending the response header Accept-CH containing the directive Sec-CH-Viewport-Width.
Accept-CH: Sec-CH-Viewport-Width
In subsequent requests, the client might send Sec-CH-Viewport-Width header:
Sec-CH-Viewport-Width: 320
Browser compatibility
See also
- Improving user privacy and developer experience with User-Agent Client Hints (developer.chrome.com)
- Device client hints
Accept-CH- HTTP Caching: Vary and
Varyheader