🔳 QR Code Generator

How QR codes carry data

A QR code is a two-dimensional barcode that stores information in a grid of black and white modules. Unlike a traditional barcode, it can be read from any angle, which is why the three large squares appear in the corners — they let a scanner establish orientation before decoding anything.

Capacity depends on the data type. A code can hold roughly 4,300 alphanumeric characters at maximum density, though in practice URLs are far shorter than that. Less data means fewer modules, larger squares, and a code that scans more reliably at distance or in poor light.

Error correction is built in

QR codes include redundant data using Reed–Solomon error correction, at one of four levels. The lowest recovers around 7% of damaged modules; the highest recovers about 30%.

This is why a code can still scan with a logo placed over the centre, or with a corner scuffed. The trade-off is that higher error correction consumes capacity, producing a denser code for the same content. For print applications where the code may be damaged or partially obscured, the higher levels are worth the density.

Making codes that actually scan

Size. A useful rule is that the code should be at least one tenth of the scanning distance. A poster read from two metres needs a code around twenty centimetres across.

Quiet zone. Leave clear space equal to four modules around all edges. Codes crammed against other artwork frequently fail to decode.

Contrast. Dark on light, always. Inverting the colours breaks many scanners, and low-contrast pairings such as mid-grey on white are unreliable under poor lighting.

Test before printing. Scan the final artwork with several phones, including at least one older device, before committing to a print run.

A note on safety

A QR code is opaque to the human eye — you cannot tell where it leads until you scan it. That property has been exploited in "quishing" attacks, where fraudulent codes are stuck over legitimate ones on parking meters, restaurant tables, and payment terminals.

Most phone cameras now preview the destination URL before opening it. Read that preview, particularly when the code leads to anything involving payment or login credentials, and be sceptical of codes on stickers that look added after the fact.

Common questions

Do QR codes expire?

A static code encodes the data directly and never expires. A dynamic code from a marketing service encodes a redirect URL, and that redirect stops working if the service account lapses.

Can I edit a code after printing?

Not a static one — the destination is physically encoded in the pattern. Only dynamic codes can be repointed later.

What else can a code contain besides a link?

Plain text, Wi-Fi credentials, contact cards, calendar events, and payment strings are all common, each using a defined text format that the scanning app recognises.