Clear explanations, a diagram on every page, and real codes you can scan with your phone. Start with the fundamentals or jump to what you need.
What a QR code is, how it works, and the words you will meet everywhere else.
A QR code is text stored as a grid of dark and light squares called modules.
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A dynamic code records each scan's time, the country from the phone's network address, and the device family from the browser's user agent. It never learns who scanned.
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Seventy-odd QR code terms, A to Z, each defined in a sentence or two.
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A 1D barcode stores a dozen digits in stripes and needs a laser or line scanner. A 2D code stores thousands of characters in a grid and a phone camera reads it.
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A static code stores the destination in the squares. It never expires and needs no account.
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A QR code is a short piece of text, usually a web address, drawn as dark and light squares.
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Versions, capacity, error correction, encoding and masking, explained with pictures.
A mask is a fixed pattern XORed over the data so the code has no big blank areas or fake finder patterns.
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Text is stored as a mode indicator, a character count, then the data bits.
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Error correction adds spare codewords so a scanner can repair modules it read wrongly.
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There are 40 versions. Version 1 is 21 by 21 modules; each step adds 4 a side up to 177 at version 40.
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From a Toyota parts factory in 1994 to payments, protests and the Moon.
Data Matrix, Aztec, PDF417 and MaxiCode are open ISO standards older than or contemporary with the QR code, each dominant in one niche.
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Masahiro Hara's two-person team at Denso released the QR code in 1994 to track car parts; the finder pattern came from a Go board.
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Quishing, sticker scams and what a trustworthy scanner does with your data.
A QR code on its own excludes blind users, many wheelchair users and anyone without a smartphone.
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A QR code cannot infect a phone. The danger is the link or action it carries, which you cannot see until you scan.
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ISO 18004, GS1 Sunrise 2027, digital product passports, payment QR formats.
From 18 February 2027, EU batteries for vehicles and industry need a QR code opening a battery passport.
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ISO/IEC 18004 defines the QR code. Editions came in 2000, 2006, 2015 and 2024; a fifth is in draft.
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A payment QR code carries either the payee's details (merchant-presented) or a one-time token for the payer's account (consumer-presented).
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Denso Wave patented the QR code but waived its rights for any code that follows the JIS and ISO standards. Nothing to pay.
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The code your phone reads is QR Model 2, standardised as ISO/IEC 18004.
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A QR code can carry a signed credential itself, or a one-time link that lets a verifier request one from your wallet.
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GS1 Digital Link puts the product number, batch, expiry and serial into a web address that a QR code carries.
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Records, art, adverts, films, stamps and other codes worth knowing about.
The largest scannable QR code was a 29,000 square metre corn maze in Alberta; the smallest measures under 2 square micrometres.
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QR codes are not dead, cannot run out, do not expire and cannot hack a phone by themselves.
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India had 657.9 million UPI QR codes at the end of FY25, up 91.5% in a year (RBI data).
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