About QR Codes: How They Work

What a QR code is

A QR code, short for Quick Response code, is a two dimensional barcode. Where an old fashioned barcode stores a handful of digits in a row of lines, a QR code stores data in a grid of black and white squares called modules. That grid can be read from any angle, which is why a phone camera locks onto it so quickly. The three large squares in the corners are finding patterns that tell the scanner where the code is and how it is rotated, and the rest of the grid carries the actual data plus information the scanner uses to check and repair it.

The data inside is usually a small piece of text. Most often that text is a web address, but it can just as easily be a phone number, an email, Wi-Fi credentials, a contact card, or a plain message. When you scan a link QR code, your phone reads the address and offers to open it. There is nothing to install for the person scanning, since modern iPhone and Android cameras recognize codes on their own.

Static vs dynamic QR codes

This is the most important distinction to understand. A static QR code has the destination written directly into the pattern. It works forever and needs no service behind it, but it can never be changed. If the link breaks or the file moves, the printed code is dead and you have to make a new one.

A dynamic QR code is smarter. Instead of the final destination, the pattern encodes a short redirect address. When someone scans it, they hit that redirect and are forwarded to wherever you currently point it. Because the pattern never changes, you can print the code once and update the destination as many times as you want. This is what makes an editable QR code so useful for anything that goes to print, from packaging to posters.

The redirect also creates a moment where each scan can be counted. That is how a trackable QR code records total scans, scans over time, and the mix of devices people used, without asking anyone to do anything extra.

Error correction: why a scuffed code still works

QR codes have a clever safety net built in. When the code is generated, extra data is added using a method called Reed Solomon error correction, the same family of math used on CDs and in deep space transmissions. This redundancy means a scanner can rebuild the original message even when part of the code is dirty, torn, or covered.

There are four correction levels, usually labeled L, M, Q, and H, that can recover roughly 7, 15, 25, and 30 percent of the code respectively. Higher levels survive more damage but pack the modules more densely, so the code needs to be printed larger or scanned closer. It is also the reason a logo can sit in the middle of a code without breaking it: the missing area is treated like damage and reconstructed from the surrounding data.

Everyday uses

QR codes earn their keep anywhere the physical world meets a screen. A restaurant links a PDF menu so it can update prices without reprinting. A shop puts a Wi-Fi code on the wall so customers connect without asking for the password. A conference badge carries a contact card so people swap details with one scan. Product packaging links a manual, a how to video, or a registration page. Marketers add a code to print ads and use the scan data to see which placements actually work.

The common thread is convenience for the person scanning and flexibility for the person who made the code. With dynamic codes you keep control after the code is out in the world, which is exactly why so many teams choose them over static ones.

Getting started

Creating a code takes a couple of minutes. Choose what you want to share, generate the code, and download it as a PNG or SVG in your own colors. Browse every QR code type to pick a starting point, or if you have a code in hand and want to read it, use the QR code decoder. Common questions are answered on the QR code FAQ.