AVIF is usually smallest, WebP is the safe middle ground and JPEG still works everywhere. Here’s when to use each, and where JPEG XL fits now.

srcset lists the image files you have, and sizes says how wide the image will display. Get both right and every screen downloads the smallest sharp file.

PageSpeed Insights merged its old image warnings into one insight. Here’s what Improve image delivery measures, and how to fix each image it flags.