Two modern formats, one step apart
WebP and AVIF are both built for the web, which makes this a narrower conversion than most on this site. People usually arrive for one of two reasons: a build pipeline, CMS, or client spec that has standardized on AVIF, or a set of WebP assets that still feels heavier than it needs to be. AVIF is the newer of the two and generally compresses harder at matching quality, so files do get smaller — just not by the dramatic margin you see when the source is a PNG or a bitmap.
Animation does not survive
This converter writes still images only. An animated WebP is decoded to its first frame, and that frame is what becomes your AVIF — the remaining frames are dropped, and the saved file gives no hint that they existed. Check whether your source moves before converting a batch. Static WebP files, including ones with transparency, convert cleanly: the alpha channel carries over to AVIF intact.
Cost, and whether it is worth it
AVIF is written by a WebAssembly module of roughly 3.4 MB, downloaded on your first AVIF conversion and cached afterwards, and it is the slowest encoder offered here. Since WebP is already a well-compressed format, weigh the gain against the effort: for a handful of images the saving may not justify a second lossy re-encode, while for a large asset library it usually does. The work happens in your browser either way — three files at a time, before and after sizes on every row, no upload, and no cap on how many you run through.