What happens on browsers that can't open WebP or AVIF?

Every visitor always gets a working image — automatically, with nothing to configure.

In practice the fallback rarely triggers. WebP and AVIF are supported by every current major browser: Chrome, Edge, Firefox, Safari, Opera, and Samsung Internet. WebP support is effectively universal; AVIF has been standard in every current major browser for years, with the gap limited to older devices that have never updated. If you want exact, up-to-date figures, see WebP support and AVIF support on Can I Use.

How the fallback works

The fallback depends on your delivery mode, but the result is the same: a browser that can't open WebP or AVIF gets your optimized JPEG or PNG.

• Picture tag mode (the default). Each image lists its formats in order, modern first and the JPEG or PNG last. The browser downloads the first format it understands and ignores the rest. A browser that understands none of the modern formats simply loads the JPEG or PNG. This is standard browser behavior, not a trick, so it is reliable everywhere.
• Server rewrite mode. Your server checks the Accept header the browser sends and returns WebP or AVIF only when the browser asks for one. Otherwise it returns the JPEG or PNG.

When a modern browser still gets the JPEG or PNG

Sometimes a perfectly modern browser receives the JPEG or PNG anyway. The usual reasons are harmless:

• The image hasn't been optimized yet, so no WebP or AVIF version exists.
• A modern version wasn't created for that exact size, so that size falls back to the JPEG or PNG.
• Delivery is set to None.

See also

• How does WebP and AVIF delivery work?
• Which delivery method should I use?