Topics Technology and the internet

How do QR codes work?

A QR code is a printed pattern of black and white squares that stores a short piece of data, most often a web address, in a form a camera can read. Your phone photographs the pattern, finds three large square markers in the corners to work out its size and angle, then reads the squares as ones and zeros and turns them back into text. Your phone then decides what to do with that text, such as offering to open a link.

What makes it interesting is how forgiving the design is. QR codes include built-in error correction, so a scuffed, partly covered or slightly blurry code can still scan. The idea comes from math used to repair data in other settings, and it is why some codes can carry a small logo in the middle. The code itself does not contain a website. It contains text, and the link lives wherever the text points.

An episode would walk through this slowly: the grid, the corner markers, the error correction, and what a code can and cannot do. It would also cover the safety side, since a printed code hides its destination until you scan it. bre is an app whose hosts are AI, so they can be wrong, and you can press Talk to ask a question mid-episode.

What a bre episode would cover

An outline of the episode bre would make for this question. Every episode is written fresh when you ask, so yours will differ.

  1. What is actually in the squaresA QR code is a grid of dark and light modules that stand for bits. Together they spell out a short string of text, often a web address.
  2. Why there are three big corner squaresThose markers let a camera find the code, judge its size and correct for tilt, so you can scan from an awkward angle.
  3. How a code survives damageError correction adds extra data, so the reader can rebuild missing pieces. That is why a smudge or a small logo often does not break it.
  4. From pattern to linkYour phone decodes the bits into text and then acts on it. The code is not a website, only a note that points to one.
  5. Where QR codes came fromThey were invented in Japan in the 1990s to track car parts in factories, as a faster-scanning alternative to ordinary barcodes.
  6. Scanning safelyYou cannot read a destination by looking at a code. We cover how to explain the risk of fake codes, and what phones show before opening a link.

How the episode might open

A sample exchange between two of bre’s AI hosts, bre and Cal. Both are AI; this is written by AI, as every bre episode is.

  1. breAI host

    Okay, picture a sticker on a restaurant table. Black and white squares, no words. You point your phone at it and a menu appears. Where was the menu hiding?

  2. CalAI host

    Honestly, I assumed the menu was in the squares. Like a tiny file. Is it?

  3. breAI host

    No. The squares hold a short line of text, usually a web address. The menu lives on a server somewhere. The code is just a very sturdy note that says where to look.

  4. CalAI host

    Hold on, how does that actually work? A camera sees a smudgy grid and somehow gets letters out of it. Where do you even start reading?

  5. breAI host

    With the three big squares in the corners. They tell the camera where the code begins, how big it is and which way it is tilted. Then it reads the little squares like ones and zeros.

  6. CalAI host

    So the corners are like the 'you are here' arrow on a mall map. And everything else is the actual message, packed in tight.

  7. breAI host

    Pretty much. And here's the part nobody tells you: some of those squares are not message at all. They are backup.

  8. CalAI host

    Backup for what? Coffee spills? Because that is my main threat model.

  9. breAI host

    Exactly that. Spills, scratches, a logo slapped in the middle. Let's start there.

Questions people also ask

Do QR codes contain websites?
Not exactly. A QR code stores text, and that text is often a web address. Your phone reads the text and offers to open the link. The website itself is stored elsewhere, which is why a code can point to a page that later changes.
Why can a damaged QR code still scan?
QR codes include extra error-correction data, built with math that lets a reader rebuild missing parts. Depending on the setting chosen when the code is made, a portion of it can be hidden or damaged and still decode. Too much damage will still break it.
Who invented the QR code?
The QR code was created in Japan in the 1990s by a company making car parts, Denso Wave, to track items in manufacturing. It was designed to be read quickly and to hold more data than a standard barcode. It later spread far beyond factories.
Are QR codes safe to scan?
Scanning is generally just reading text, but the text can point to a harmful site, and you cannot tell by looking. This page explains the risk rather than advising you. Many phones show the link before opening it, which lets you check the address first.

Related topics

More: all 300 topics, technology and the internet, or the longer reads on /learn.

bre’s hosts are AI, and every episode is generated, so they can be wrong: check anything that matters. This page outlines what an episode would cover. It is for interest and learning, not medical, financial or legal advice.