Encoding · Design
What Is a QR Code? A Complete Guide
QR (Quick Response) codes were invented in 1994 by Denso Wave to track car parts. Thirty years later, they're on menus, ads, boarding passes, and payment terminals worldwide. Here's how they actually work and how to design ones that scan reliably.
Anatomy of a QR code
- Position markers — the three big corner squares. They tell scanners the orientation.
- Alignment marker — the smaller square (bottom-right area) that corrects perspective distortion.
- Timing pattern — alternating black/white line between position markers, used to calibrate cell size.
- Data cells — the encoded payload, plus Reed-Solomon error correction.
- Quiet zone — the empty border (minimum 4 cells wide) that isolates the code from background clutter.
Error correction levels
| Level | Recovery | Use case |
|---|---|---|
| L (Low) | ~7% | Clean, high-contrast environments |
| M (Medium) | ~15% | Default for most codes |
| Q (Quartile) | ~25% | Print with wear expected |
| H (High) | ~30% | With logo overlay or on rough surfaces |
Static vs dynamic
A static code encodes the destination directly — the URL is baked into the pixels. It works forever and can't be tracked. A dynamic code encodes a short redirect URL (like qr.example/abc123) that a service resolves to the real destination. Dynamic codes let you change the destination after printing and add scan analytics — but they stop working if the redirect service disappears.
Security: the "quishing" threat
QR phishing ("quishing") stickers overlay legitimate codes on parking meters, restaurant tables, and transit posters, sending scanners to lookalike payment pages. Always preview the URL before opening, and be extra suspicious of codes that ask for card details or logins.
Design tips that keep codes scannable
- Keep the quiet zone (white border) — it's not optional.
- High contrast: black on white scans fastest. Dark-on-dark or pale gradients often fail.
- Minimum print size ~2×2 cm for short URLs, larger for dense data.
- Logo overlay: use error correction level H and keep the logo under 25% of the code area.
- Test scan from your target distance — a wall poster is not the same as a business card.
Try it on Toolzer
- QR Code Generator — free, no signup, exports SVG and PNG.
- QR Code Scanner — scan codes from images or webcam.
- Barcode Generator — classic 1D barcodes for products and shipping.
- URL Safety Checker — verify a scanned link before opening.
Frequently asked questions
How much data can a QR code hold?+
A Version 40 (largest) QR code can hold up to 4,296 alphanumeric characters or 2,953 bytes. Practical scans work best under 300 characters — beyond that, scanners struggle with high-density codes.
Do QR codes expire?+
Static QR codes (encoding URLs or text directly) never expire. Dynamic QR codes (which redirect through a tracking service) stop working if the service shuts down or you don't renew a subscription.
Can QR codes contain viruses?+
The QR code itself is just data — but it can encode a link to a malicious page. Always preview the URL before opening, especially on stickers placed in public (parking meters, restaurant tables) where scammers overlay legitimate codes.
Why do some QR codes have a logo in the middle?+
QR codes include error correction (up to 30% of the code can be damaged and still readable). You can safely overlay a logo covering up to ~25% of the center if the code uses high error correction (level H).
What's the difference between QR and barcode?+
1D barcodes hold ~20 characters and only scan in one direction. QR codes are 2D matrices, hold thousands of characters, and scan from any angle — which is why they replaced barcodes for most consumer uses.