Point it at a link and get a code you can print on a flyer, a poster or a
merch tag. Nothing uploads anywhere — it is generated in this browser and saved straight
to your device.
The link
How it is built
How much of the code can be damaged and still scan. Q is a good
default for anything printed; go to H if you put a logo in the middle, because the
logo is the damage.
The blank margin. The spec asks for 4; below that, scanners start to
struggle to find the code at all.