A favicon is the small icon in browser tabs, bookmarks, history and search results, and it also becomes the app icon when someone adds your site to a phone's home screen. Different places ask for different files, so a complete set is more than one image.
This generator takes one PNG, JPG, SVG or WebP and shows a large preview of your icon as soon as you choose it, a browser-tab mock in light and dark, and the icon at its real 16, 32 and 48 px sizes. Fit the image with padding or crop it to fill, keep a transparent background or pick a colour, and choose square, rounded or circular corners. You then get favicon.ico (16, 32 and 48 px inside), favicon-16x16.png, favicon-32x32.png, apple-touch-icon.png (180 px), android-chrome-192x192.png, android-chrome-512x512.png, a site.webmanifest and the HTML to paste into your page's head, all in one ZIP.
Limits: detailed logos and long wordmarks become unreadable at 16 px. A simple mark or a single letter works better, and the real-size preview shows you how it will look. For a sharp 512 px icon start from an SVG or an image at least 512 px wide. The Apple touch icon always gets a solid background, because iPhones show transparent areas as black. Google picks which favicon to show in search results itself and can take days to update it.