In short
This tool changes the format of images between JPG, PNG and WebP, several at a time: to send a WebP image to someone whose software cannot read it, or to turn a PNG screenshot into a JPG. Dimensions are kept and the encoding quality stays high, because the aim is not to compress; for that, there is “Compress images”. JPG does not support transparency: transparent areas become white. EXIF data, GPS location included, is removed. Images over 100 megapixels are refused, and older versions of Safari cannot create WebP files. Several converted images are bundled in a ZIP. The conversion happens in your browser.