#qr-codes — How QR codes work, what scans, and the design rules most generators skip

A QR code is a 2D grid of dark and light cells that encodes data — usually a URL, sometimes a vCard or a WiFi network or a plain message. Phones decode them by sampling the centre of each cell, asking "darker than threshold or lighter than threshold," and reconstructing the bits with help from built-in error correction. That's the technology. The interesting questions are everywhere else.

Should you use a static QR code (the URL baked into the print) or a dynamic one (the QR encodes a short link you can repoint later)? Round modules look better — but does the contrast loss break the scan? When does a centre logo become too big? What changes when the code lives outdoors versus indoors, on glossy vinyl versus matte paper, on packaging at 1cm versus a billboard at 30 metres?

These posts answer the questions in detail. Some are anatomy. Some are format-specific (vCard for business cards, WiFi for guest networks, calendar events for invitations). Some are design — round modules, custom shapes, brand colours that actually pass the contrast threshold. Some are about real-world conditions: outdoor advertising, surface materials, scan distance and module size math.

If you're picking a QR designer, generating codes for a campaign, or evaluating which generator your team should standardise on, these are the posts that cover the constraints the previews skip.