Generating the black-and-white pattern is the easy part. Reliability depends on what you encode, how densely it is packed, the contrast, the printed size and the surface where people will scan it. A beautiful code that fails under ordinary lighting is still a failed code.

Keep payloads short when you can. Test URL, Wi-Fi, vCard, SMS and email codes on more than one device before they go onto packaging, signage or printed material. For barcodes, verify that the receiving system expects the symbology you generated.

Before printing

Scan from the distance a real user will stand.
Try a second phone and avoid trimming the quiet area around the code.
Check the decoded destination—not merely whether the camera recognised something.

When a code becomes fragile

Long payloads create denser patterns.
Low contrast, glossy surfaces and aggressive resizing make recognition harder.

For practical failure cases, see the QR code reliability guide.