Guides
12 guides, about 10,000 words, on how codes actually work: what the pattern contains, how error correction behaves, how big to print, why a code that looks fine on screen fails on press, and which barcode format belongs on which label.
They are written for the person doing the work rather than as an advertisement. Nothing here needs an account, and most of it applies whichever tool you use to make the code.
Anatomy of a QR code
Most of a QR code is not your data. Roughly a quarter of a small symbol is scaffolding that exists so a camera can find the code, work out how big it is, tell which way up it is, and know how to read the rest. Here is what each piece does.
Error correction levels, and what they really buy you
Every QR code carries redundant data so it can be read when part of it is unreadable. You choose how much. The four levels are widely quoted as "7%, 15%, 25% and 30% damage tolerance", and that shorthand is misleading in a way that matters when you are placing a logo.
How big to print a QR code
There is a rule of thumb: a code reads from about ten times its own width. It is a good rule and it is a summary of something more useful, which is that the only dimension a scanner cares about is the size of one module.
Printing codes that survive the press
A code is a measuring instrument disguised as a graphic. Everything a printer does to make artwork look good on paper, spreading ink, adding gloss, curving the substrate, works against the thing a scanner is trying to measure.
Color, contrast and why scanners disagree with your eyes
A code can be almost any two colors, as long as a scanner can tell which is which. That turns out to be a question about brightness and wavelength rather than about color, and it is why some combinations that look bold to a designer are unreadable at a till.
Why a code will not scan
Almost every scanning failure is one of six things, and they are worth checking in a particular order, because the first two questions are free and they decide which of the remaining four is worth your time.
QR code security, honestly
The scary headline is that QR codes can infect your phone. They cannot: a QR code is text, and text does not execute. The real risks are more mundane and more effective, and they work on the person rather than the device.
What the text inside a QR code actually looks like
A QR code stores characters and nothing else. When a phone offers to join a network or save a contact, it is pattern-matching on a prefix in that text. Here are the formats, and the places they behave differently on iOS and Android.
Four two-dimensional codes, and why each exists
QR is not the only two-dimensional barcode, and in several industries it is not the usual one. The differences between the four you will meet come down to one design decision each, and that decision explains where you find them.
Which barcode format do you actually need
There are dozens of barcode symbologies and only a handful you will ever choose between. The choice is almost never about the data. It is about where the label goes, who scans it, and whether the number has to mean something to somebody else.
GS1 identifiers, and how one barcode carries several facts
A retail barcode holds one number. A logistics barcode often needs to hold four or five, with no ambiguity about which is which and no shared database to look them up in. Application Identifiers are how that works, and they are a surprisingly elegant piece of design.
Check digits, worked by hand
The last digit of a retail barcode is not part of the product number. It is arithmetic on the digits before it, and it exists so that a scanner which misreads one bar produces an error rather than somebody else's product.