How QR Codes Work: From Printed Squares to a Useful Action
Understand what a QR image stores, why longer content makes denser codes, and how to separate a decoding problem from a destination problem.
The image holds a message, not the whole website
When a QR contains a website address, it stores the characters of that address. Your scanner first recovers those characters; your browser then requests the page. These are separate steps. A phone can recognise a code while the destination is offline, and a plain-text code can be decoded without needing to fetch a web page.
Other payloads describe actions. A tel: link can offer a phone call, a contact card can offer to save details, and an event payload can offer a calendar import. The receiving app decides which actions it supports and may ask for confirmation. Creating the QR does not send a message, make a call or add an event automatically.
How a scanner finds the grid
The large corner markers help a reader locate and orient the symbol. Additional structural patterns help it interpret the grid. The remaining pattern includes encoded content, format information and redundant data for error correction. It is not accurate to treat every visible square as one independent character or user-data bit.
Real photographs can be blurred, angled or unevenly lit. Scanners must distinguish the small modules from their background and locate the symbol boundary. Dark modules on a light, uncluttered background are a useful starting point. Rotating a code is different from expecting a severely curved, reflective or damaged print to scan reliably.
Why adding text can make a code harder to print
QR versions have different grid sizes. DENSO WAVE describes standard versions from 21 to 177 modules per side. More content can require a larger grid; character encoding and error correction also affect capacity. If you keep the same physical print width, a denser grid leaves less space for each module.
Try a practical comparison: create a short URL code, then a contact card with a long address and notes. Use the same image size and inspect the previews. This is an exercise you can repeat, not a claim that every extra character changes the version. The DENSO WAVE version reference explains the relationship between capacity and grid size.
Error correction helps, but it is not spare space for a logo
Extra information allows some lost or corrupted data to be recovered. The available correction depends on the level and the kind of damage. The familiar highest-level percentage describes codewords, not a guarantee that you can hide an arbitrary portion of the image. Covering a positioning marker can cause a different problem from damaging some data modules.
Keep logos modest and test the complete artwork. A higher correction level can also increase density, so it does not remove the need for adequate print size. See DENSO WAVE's error-correction explanation for the technical distinction.
Static and dynamic refer to what happens after decoding
A static payload is fixed in the exported pattern. A dynamic service commonly puts its redirect address in that pattern and lets its server change the onward destination. A website you control can also keep the same address while its page content changes. None of these approaches physically edits an already printed pattern.
This site's generator creates static payloads. Its local projects make it easier to return to a design, but editing a saved project creates new artwork. It does not update copies that were already printed.
A three-stage troubleshooting test
- Decode the exported image. Use the reader to inspect the actual content. If it fails, simplify colours or the logo and check the border.
- Test the action. If a URL is correct, open it independently. If a contact or event payload is correct, try a compatible receiving app or its downloadable file.
- Test the physical copy. Scan at the intended distance, with normal lighting and on the actual material. A screenshot test cannot reproduce glare, ink spread or a damaged sticker.
The generator includes automatic scan verification and physical-size guidance. Those checks help identify problems; neither is a guarantee of safety or universal scanner support.