Content determines density
A short URL generally requires fewer modules than a long vCard or multi-line text. Adding data makes modules smaller at the same overall size. Keep the payload concise and accurate.
Choose SVG when you need scalable artwork. PNG has a fixed pixel grid; enlarging a small raster image can blur its edges. Do not stretch either format unevenly.
Keep a clear quiet zone
A QR code needs a clear light margin around its square. Preserve at least the standard four-module quiet zone in your artwork; avoid placing borders or text inside that region.
Use dark modules on a light background. Decorative logos, overlays, transparent backgrounds and inverted colours can reduce reliability, even when the onscreen design looks attractive.
Test at the intended distance
Make a sample at the actual finished size. Scan from where people will stand or sit, in typical light, using more than one phone. A successful close-up screen scan does not replace a print test.
For a dense code or a distant sign, enlarge it or reduce the content. Avoid a universal millimetre promise; compare practical test results in the real placement.
Final checklist
Check the decoded destination or data, verify the clear margin, inspect sharpness, test the printed stock and keep a clickable or readable alternative where appropriate.
WiFi tests should use a device not already connected. vCard tests should check imported fields. Event tests should include submitting the form, not only opening its URL.