QR codes are everywhere — menus, business cards, product packaging, conference badges. They're fast, readable by any smartphone, and carry a surprising amount of data. Here's how they actually work, and how to generate one without installing anything.
What Is a QR Code?
QR stands for Quick Response. It's a two-dimensional matrix barcode that encodes data as a pattern of black and white squares. Unlike a traditional barcode (which only encodes data horizontally), a QR code encodes data in two dimensions — which is why it can hold much more information.
The format was invented by Denso Wave in 1994 for tracking vehicle parts during manufacturing. It's now part of an ISO standard (ISO/IEC 18004) and is freely usable without royalty.
What Can a QR Code Store?
| Data Type | Max Characters (approx) |
|---|---|
| Numeric only | 7,089 |
| Alphanumeric | 4,296 |
| Binary (any data) | 2,953 bytes |
| Kanji/Japanese | 1,817 |
In practice, most QR codes store:
- URLs (most common)
- Plain text
- Contact cards (vCard format)
- Email addresses or phone numbers
- WiFi credentials (
WIFI:T:WPA;S:NetworkName;P:password;;)
How Error Correction Works
QR codes have built-in error correction. Even if part of the code is damaged or covered, it can still be read. There are four levels:
| Level | Recovery Capability |
|---|---|
| L (Low) | ~7% damage |
| M (Medium) | ~15% damage |
| Q (Quartile) | ~25% damage |
| H (High) | ~30% damage |
Higher error correction = larger QR code for the same data. Use H if you're printing the code on a surface that might get scratched or wet. Use L for digital-only use where the code will always be pristine.
Do QR Codes Expire?
No. A QR code is just encoded data — it doesn't expire on its own. If the URL inside it goes down or changes, the code stops working, but that's a URL problem, not a QR code problem.
Some services (like QR code tracking platforms) use short redirect URLs inside the code and can change the destination later. But a QR code generated from a direct URL (like https://snappytools.app) is permanent.
Generating a QR Code
You don't need a paid service for basic QR codes. The open-source qrcode library for JavaScript (via qrcodejs) and Python (qrcode package) can generate codes client-side with no server needed.
SnappyTools' QR code generator generates codes in your browser, with no data uploaded, no signup required, and download as PNG in one click.
``javascript
// Client-side QR generation with qrcodejs
const qr = new QRCode(document.getElementById("qr"), {
text: "https://snappytools.app",
width: 256,
height: 256,
colorDark: "#000000",
colorLight: "#ffffff",
correctLevel: QRCode.CorrectLevel.H
});
``
Best Practices
Size: Print QR codes at a minimum of 2.5 cm × 2.5 cm (1 inch) for reliable scanning. Larger is better.
Contrast: Black on white is optimal. Light on dark works but is less reliable. Avoid pastel combinations.
Quiet zone: Leave a margin of 4 cells around the code (the "quiet zone"). Without it, some scanners fail.
Test first: Always scan your QR code from multiple devices and angles before printing. What looks correct visually may still fail if the contrast or size is off.
Summary
QR codes are simple, permanent, and free to generate. The key variables are: what data you're encoding, the error correction level (higher for physical print), and the output size. Use snappytools.app/qr-code-generator/ to generate a code in seconds — no account, no data stored.
Originally published at https://snappytools.app/qr-code-generator/