Oversized images are the most common reason a site feels slow, and the easiest thing to fix.
Start with dimensions appropriate to the image's actual display area. Compare a JPG and WebP at the same visible size, and check text and gradients. This tool exports files; it does not create srcset HTML, responsive variants or a CDN.
The starting maximum width is 1920 pixels. Choose Keep original size when dimensions must remain unchanged.
JPG and WebP use the quality control. PNG ignores it; compare actual sizes because results can be larger.
Work out the widest a picture is ever displayed on your page, and make the file about twice that wide so it stays sharp on high density screens. A picture shown at 800 pixels is well served by a 1600 pixel file, and one shown full width rarely needs more than 1920.
Run the whole folder through at once with the same settings, choose WebP for the smallest files, and check a few pictures on the live page afterwards. The size shown for each file lets you spot any that are still too heavy.
Choose Keep original size instead of the default maximum width. JPG or WebP quality changes can reduce bytes but also affect visual detail.
JPG, PNG and WebP always open. Other types depend on your browser, so convert them first with Convert format. A very large photo can run out of memory on a phone, so try a computer.
1920 pixels is the default and is enough for almost every screen. Wider than that adds weight without a visible gain.