...You feed it an image (png, jpg, gif), it will crop it if its not a square, then it will resize and convert it to the correct format.
I have support for these:
- Windows PC Exe Programs - 16×16, 32×32, 48×48, 256×256 .ico bundled
- Website Favicon - 32x32 .ico
- Android Phone Apps - 192x192 .png
- Progressive Web Apps (PWA) - 512x512 .png
I recommend uploading images atleast 512x512px tall/wide, unless you're doing pixel perfect icons and just want an easier 'convert to .ico format' tool.
(Source code is included as it is a standalone offline html file that works in any modern web browser.)