QR Code Error Detection

QR code error detection refers to the mathematical mechanisms built into QR codes that let scanners tell whether the data they read is intact. The data area of a QR code is built from codewords (one codeword equals 8 bits), and Reed-Solomon error correction is added to that area so damaged codewords can be restored. Reed-Solomon corrects at the byte level, which suits errors concentrated in one spot, such as a smudge or a torn corner. Four error correction levels exist: L (7%), M (15%), Q (25%), and H (30%), representing the percentage of codewords that can be restored if damaged. Higher levels increase the code's physical size but improve scan reliability. For URL shortening services that generate QR codes, error detection is critical. Short URLs minimize the data payload, allowing higher error correction levels without excessive code density. This helps codes stay readable when they are printed on curved surfaces, partially covered, or displayed in poor lighting conditions.