When WebP is the more practical target
Saving a picture from a modern website often drops an .avif file on your disk, and AVIF is still the format most likely to be turned away — by an image editor, a CMS uploader, or a colleague on an older machine. WebP sits one generation back and is handled far more widely: every current browser renders it, and most tools that reject AVIF accept a WebP without complaint. It also keeps transparency, which makes it the better target than JPG whenever your AVIF has a cut-out background.
No encoder to download
WebP is one of the three formats browsers encode natively, so this direction is much quicker than the reverse one. A Web Worker decodes the AVIF with the browser’s built-in decoder and writes a WebP at 92% quality — high enough to be visually indistinguishable from the source in normal use. There is nothing to fetch first and nothing to install, so even a long queue moves at the speed of your processor.
Expect a slightly larger file
AVIF compresses more aggressively than WebP, so the file you get back will usually be bigger than the AVIF you started with. That is the price of wider compatibility, not a fault in the conversion. Both formats are lossy, which also makes this a second encoding pass; the visible difference is minimal at 92%, but keep the AVIF if you want the smallest possible copy. Batches run three at a time, every row shows both sizes, and finished files download individually or as one ZIP. Nothing is uploaded at any stage.