ICO converter
A favicon is built in your browser from your image, so it never leaves your device. The icon sizes are rendered and packed locally, free.
What is ICO?
ICO is the Windows icon container, and the format browsers still expect for a favicon. One .ico holds the same picture at several sizes, so the system can pick the right one for a tab, a taskbar, or the desktop. Building one means resizing a source image to those standard sizes and packing them together.