Before you print
How big should it be?
Rule of thumb: printed width ≥ scanning distance ÷ 10. Pick the surface above and the studio sizes the code for you, then checks the printed module size against what a press can actually hold.
Questions people actually ask
Mostly developers and operations teams: provisioning IoT devices, labeling inventory and assets with structured data, passing config into kiosk apps, or moving small payloads between machines with no network involved. Your own scanner app reads the JSON and acts on it.
Roughly 2,900 bytes at the lowest error-correction level, and less as you raise error correction to survive logos and print damage. Keep payloads compact — short keys, no pretty-printing — and stay under about 1 KB for reliable everyday scanning.
The phone shows the JSON as plain text — it will not parse or act on it. JSON codes are meant for your own app or scanner integration; for human-facing codes, use a URL type instead.
The JSON is validated as you type so you never ship a malformed payload, and everything runs in your browser — nothing is uploaded to UseQR. Free, no signup, no limits.
Want the detail? How json QR codes work — the payload format, what scanners do with it, and where it breaks.