What a QR code really is

A QR code is text written as a pattern of squares (ISO/IEC 18004). There is no app or server connection inside — just a plain string, most often a URL. The phone reads the string and does with it what it normally does with that kind of content: opens a page, offers to add a contact, or joins a Wi-Fi network. The “What exactly is inside the code” panel shows that string in full.

Static and “dynamic” QR codes

Every QR code is static: once printed, it never changes. The “dynamic” codes from commercial services are ordinary codes that contain a short address on the service's domain. The service redirects that address to the destination you can change in a dashboard. It's convenient, but the code then depends on someone else's domain and subscription — once the account lapses, printed codes may stop working (it depends on that service's terms).

You can get the same effect without a middleman: the code points to an address on your own domain, and you decide what to show there. You change the page content or the redirect; the code stays the same.

Example: a sticker on a fridge

A manufacturer prints a code with the address https://producent.pl/s/SN-48213 on the rating plate. On the day of purchase the page shows setup instructions. After two years, a maintenance guide and filters for that model; after five, a warranty extension offer. The code and the sticker are the same — only the server's response changes. This does require the page to recognize the number in the address and know how old the product is — that's your website's job, not the generator's.

What to plan so the code lasts for years

• Domain — renew it. Registration is a recurring cost, and the code works only as long as the domain does.
• A stable address scheme — choose the structure (e.g. /s/{number}) before printing the first sticker, and don't change it afterwards.
• A short address — a shorter string means a sparser pattern, easier to scan from a small print.
• Temporary redirects — if you point elsewhere, use a 302 or 307 redirect rather than a permanent 301: browsers cache 301s, so a change of destination may not reach people who scanned earlier.
• Measurement — a static code doesn't count scans by itself. Add UTM parameters and read the data from your own site's analytics.

Size, contrast and error correction

• Contrast — dark pattern on a light background. Only some scanners read inverted codes (light on dark).
• Margin — the standard recommends at least 4 modules of empty space around the pattern.
• Size — the 10:1 rule: width is roughly one tenth of the scanning distance. Denser codes need extra room.
• Error correction — L, M, Q and H tolerate roughly 7, 15, 25 and 30% damaged area respectively. A higher level gives a denser pattern. For stickers exposed to wear choose Q or H; for screens M is enough.
• Module styles — rounded and dots look more interesting, but not every scanner handles them equally. Always test.

Limitations of this generator

The generator creates static codes: it doesn't host redirects or count scans. It doesn't place a logo in the middle of the code — if you add one by hand in a graphics editor, use error-correction level H and test the result thoroughly. No hint in the panel replaces testing on real devices before printing a batch.

Privacy

The code is built in your browser and the data you type — including a Wi-Fi password — is not sent anywhere. Just remember that a printed code with a password shares it with anyone who sees it.