Two things make a photo smaller here: the quality slider, which runs from 20 to 95, and the longest-side box, which scales the pixels down before anything is compressed. Use one or both. What comes back is always a JPEG, whatever you put in, and the file keeps its name with .jpg on the end.
This page loads no libraries at all. The work is done by the browser itself. Your file is read on your own machine and never sent anywhere. Open your browser’s network tab and watch while you use it.
No. Whatever goes in, a JPEG comes out. JPEG cannot hold transparency, so if you compress a PNG that has a transparent background, that background is filled with white.
The page does not predict it. You press Compress, and the before and after sizes you are shown are measured on the finished file rather than estimated. A file that is already well compressed can come back no smaller, or even bigger, and when that happens you are told so instead of being shown a saving.
It scales the picture down until neither side is longer than the number you type, and the compression happens after that. It only ever shrinks: set it larger than the picture and nothing is scaled. Leave it at 0 and the pixel size is kept as it is.
No. Each run starts again from the file you picked rather than from the previous result, so you can move the slider and press Compress as often as you like without stacking one round of JPEG loss on another.
Everything here is free and works the same way, in your browser.
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