Viewport-Width

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

The HTTP 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 Viewport-Width header appears more than once in a message the last occurrence is used.

A server has to opt-in to receive the 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 header name No

Syntax

http
Viewport-Width: <number>

Directives

<number>

The width of the user's viewport in CSS pixels, rounded up to the nearest integer.

Examples

Using Viewport-Width

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

http
Accept-CH: Viewport-Width

In subsequent requests, the client might send Viewport-Width header:

http
Viewport-Width: 320

Browser compatibility

BCD tables only load in the browser

See also