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.
Width device client hint request header field indicates the desired resource width in physical pixels — the intrinsic size of an image. The provided pixel value is a number rounded to the smallest following integer (i.e. ceiling value).
|Header type||Request header, Client hint|
|Forbidden header name||no|
The hint is particularly useful because it allows the client to request a resource that is optimal for both the screen and the layout: taking into account both the density-corrected width of the screen and the image's extrinsic size within the layout.
If the desired resource width is not known at the time of the request or the resource does not have a display width, the
Width header field can be omitted.
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
Widthheader from the client, by sending the
- Servers that opt in to the
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.
Widthwas removed from the client hints specification in draft-ietf-httpbis-client-hints-07. The proposed replacement is
Sec-CH-Width(Responsive Image Client Hints).
The width of the resource in physical pixels, rounded up to the nearest integer.
The server first needs to opt in to receive the
Width header by sending the response headers
Then on subsequent requests the client might send
Width header back:
BCD tables only load in the browser
- Improving user privacy and developer experience with User-Agent Client Hints (web.dev)
- Device client hints
- HTTP Caching > Varying responses and