A studio that checks the code still scans
Colours, a logo in the middle, rounded modules, a frame with a call to action — and a contrast check before you download, because a beautiful code that does not scan is worse than a plain one.
Design
Foreground and background colours, module and eye shapes, a logo with a quiet zone punched out behind it, and framing captions. Everything renders in the browser as you change it, so there is no round trip and no queue.
The check
Low contrast and an oversized logo are the two ways a designed code stops working, and neither is visible to a person looking at it. The studio measures the contrast ratio and how much of the symbol the logo covers, and tells you before you download rather than after you print.
Formats
PNG at print resolution, SVG for anything that will be scaled, and PDF for handing to a printer. Vector is the one to use if the code is going on anything larger than a flyer.
Design changes the appearance of the symbol, not its data. A code already on paper cannot be redesigned — only a dynamic code's destination can change after printing.