The tool, called Squoosh, lets you do just that to your images. It can compress an image saved in most Web formats, from JPEG to PNG to MozJPEG. While squooshing, you can view a 1:1 comparison of the images, to make sure you aren’t compromising too much quality. Once you’re done, fully squooshed images can be downloaded right to your computer.
The tool works offline in the browser once you’ve got it loaded and is compatible with most browsers (cue the Chrome versus Firefox debate). What’s more, Squoosh is open source, so you can see exactly how it works on GitHub.