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.
|Header type||Request header, Client hint|
|Forbidden header name||no|
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.
Viewport-Width header appears more than once in a message the last occurrence is used.
- Client Hints are accessible only on secure origins (via TLS).
- A server has to opt in to receive the
Viewport-Widthheader from the client, by sending the
- Servers that opt in to the
Viewport-Widthclient hint will typically also specify it in the
Varyheader. This informs caches that the server may send different responses based on the header value in a request.
Viewport-Widthwas removed from the original client hints specification in draft-ietf-httpbis-client-hints-07. The proposed replacement is
Sec-CH-Viewport-Width(Responsive Image Client Hints).
The width of the user's viewport in CSS pixels, rounded up to the nearest integer.
A server must first opt in to receive the
Viewport-Width header by sending the response header
Accept-CH containing the directive
Then on subsequent requests the client might send
Viewport-Width header back:
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