Contact
MeCard holds the same contact in far fewer characters than vCard, so the printed code is less dense and scans better when small. Android reads it natively; iOS support is good but not universal, so use vCard if the code has to work everywhere.
Preview
Fill in the fields and the QR code will appear here.
Held in the hand. Keep the content short, because a long URL makes this too dense.
Rendered at 300 dpi for the physical size, at 85 × 55 mm. The destination is printed in small type beneath the code so a failed scan is not a dead end.
Kept in this browser so you can reopen and edit it later. Nothing is uploaded.
Design
The blank margin scanners use to find the code's edges. Four is the specified minimum, so the slider does not go lower.