Why won't my QR code scan?
A QR code usually won't scan because it's too small for the distance, too low-contrast, has its quiet-zone margin cropped, or is blurry from low-resolution printing. Fix the size, contrast, and margin and it almost always reads.
Nearly every unscannable code comes down to one of a handful of physical problems, not the data inside it. Work through them in order (size, contrast, quiet zone, resolution, obstruction) and the code comes back to life.
If a code that used to work suddenly stopped, the problem is different: the destination behind it likely moved or died. That's covered in my QR code stopped working, and it's exactly the failure an editable code prevents.
Step by step
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Make it bigger
Print at least one-tenth as wide as the farthest scan distance. Check the scan distance to print size reference if you're unsure.
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Raise the contrast
Keep the pattern dark on a light background. Pale colors or a busy photo behind the code defeat scanners.
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Leave the quiet zone
Keep the empty margin (about four modules) around the code clear; don't crop tight to the edge.
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Use a sharp source
Print from an SVG, or a PNG at 300 DPI or higher, so the module edges stay crisp.
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Uncover the corners
Keep any logo centered and small enough that the three corner finder patterns stay clear.
See also
Never reprint a code again
A TangoQR code is an editable redirect: change where it points anytime, no reprint. Free to start.
Make your first code, free