A QR (Quick Response) code is a two-dimensional barcode that packs far more data than the familiar single-line barcode on a product — up to a few thousand characters, depending on the version and error correction level used. It was invented in 1994 by Denso Wave for tracking automotive parts, and its patent was released royalty-free, which is a large part of why it became the universal standard it is today instead of one of several competing formats.
It's not just for URLs
A QR code just encodes text — what a scanner does with that text depends entirely on its format. A plain URL opens a browser. Text prefixed tel: opens the phone dialer. mailto: opens an email composer. A specially formatted string starting with WIFI: can auto-join a Wi-Fi network. The QR code itself has no special awareness of any of this — it's the scanning app that interprets the payload and decides what action to take.
Why QR codes survive a torn corner
QR codes use Reed-Solomon error correction, the same family of algorithm used in CDs and DVDs, which encodes redundant data alongside the actual payload. Depending on the error correction level chosen (L, M, Q, or H), a QR code can remain scannable with up to roughly 7% to 30% of its area damaged or obscured — which is also why some brands get away with placing a logo in the center of a QR code without breaking it.
Higher error correction means a more robust code, but also a denser, more complex pattern for the same amount of data — there's a real tradeoff between damage resistance and how much text fits at a given physical size.
The security angle: "quishing"
Unlike a text link, you can't preview where a QR code leads before you scan it — the destination is opaque until your phone's camera decodes it. This has become an actual phishing vector ("quishing"): attackers print malicious QR code stickers over legitimate ones on parking meters, restaurant tables, or posters, banking on the fact that people who'd hesitate to click a suspicious link will scan a QR code without a second thought.
The practical defense is the same instinct you'd apply to a link: check the URL your phone shows before tapping through, especially for QR codes in public physical locations rather than ones you generated or received from a trusted source directly.
Try it
GlaeKit's QR Code Generator turns any text or URL into a downloadable QR code entirely in your browser — nothing is sent to a server.
Frequently asked questions
How much data can a QR code hold?
Up to about 4,296 alphanumeric characters at the largest standard size and lowest error correction level — though in practice, most QR codes encode a short URL or a small amount of text, since more data means a denser, harder-to-scan pattern.
Do QR codes expire?
A static QR code (like the ones generated here) never expires — it's just an image encoding fixed text, with no server or account behind it. Some commercial QR services offer "dynamic" QR codes that redirect through their own server, which can expire or be redirected later, but that's a feature of the service, not of QR codes themselves.
Can a QR code contain a virus?
The QR code itself is just text — it can't execute code. The risk is entirely in where that text (usually a URL) leads: a malicious site designed to phish credentials or exploit a browser vulnerability. Treat a scanned QR code link with the same caution as any unfamiliar link.