QR code not working — a 60-second diagnosis

A QR code fails in one of three ways. The scanner never detects it (quiet zone, contrast, size), it decodes the wrong string (bad input, tampering, a mangled image), or the destination is broken (dead URL, retired shortener, blocked network). Decode the code with a scanner that shows the raw text — that one step splits the three classes apart.

The three failure classes

"Not working" hides three different faults with three different owners:

Class	What you see	Where the fault is
1. Never detected	The camera never reacts; no banner appears	The image — quiet zone, contrast, size, blur
2. Decodes the wrong thing	A link appears, but it is wrong or garbage	The data — wrong input, tampering, a mangled file
3. Destination broken	The link opens, then errors	The URL — dead page, retired shortener, blocked network

The instinct is to re-scan harder. Diagnosis is faster.

The 60-second flow

Decode the code with a tool that shows the raw text instead of following it. Our scanner does this in the browser, from the camera or an uploaded photo.
Nothing decodes at all? Class 1 — the image is the problem.
It decodes, but the string is wrong? Class 2 — the data is the problem.
The string is right, but the link fails? Class 3 — the destination is the problem.

That single decode separates the image from the data from the destination — the split most people never make. Each class routes to its fix below.

Class 1 — the camera never finds it

Ranked by how often each is the real cause:

Quiet zone. The blank margin must be at least 4 modules on every side. Designers crowd it constantly, and without it the code is never detected at all — see quiet zone too small.
Contrast and polarity. Dark modules on a light background, with at least a 40% luminance difference. Light-on-dark and low-contrast brand colours scan on some phones and not others.
Size for the distance. Printed width must be at least scan distance ÷ 10. A 3 cm code across a lobby has no chance — see too small to scan.
Blur and damage. Upscaled raster images, heavy compression, glare, folds and worn print.

The not-scanning checklist works through all of these in priority order, with the numbers.

Class 2 — it decodes to the wrong thing

Wrong input. A typo, a missing https://, trailing whitespace or an invisible character in the pasted URL. Regenerate from a copied link, never a typed one.
Tampering. A sticker pasted over the original is the standard quishing move on parking meters, payment standees and menus. Feel the surface for a raised edge.
A design tool mangled it. Codes that were traced, redrawn, mirrored or flattened can decode to garbage. Regenerate rather than repair.

Full walkthrough: QR code opens the wrong link.

Class 3 — the code is fine, the destination is broken

The string decodes exactly as intended; the fault is at the other end:

404 or moved page — the site was rebuilt and the old path lost its redirect.
A retired link shortener — free redirect services sunset, prune links or move them behind paywalls; see shortener expired.
A lapsed domain — the worst case, because someone else can register it next; see dead domain.
A blocking network — corporate DNS filters and captive portals commonly block shortener domains wholesale.

Test the URL in a browser on mobile data, not the office WiFi, before blaming the code.

Prevent the next one

Before anything goes to print, run the artwork through our validator — it renders the code, decodes the output and checks contrast and quiet zone, which catches classes 1 and 2 in a single pass. For class 3, point printed codes at a stable path on a domain you own, and re-test the printed estate quarterly.

FAQ

Why did my QR code suddenly stop working?

A static code's pattern never changes, so a code that used to work almost always has a destination problem: a moved page, a retired shortener or a lapsed domain. Physical wear and a sticker pasted over the original are the remaining suspects.

How do I find out what is wrong with my QR code?

Decode it with a scanner that shows the raw text rather than opening it. No decode means an image problem, a wrong string means a data problem, and a correct string with a failing link means a destination problem.

Do QR codes expire?

The pattern itself never expires — it is printed geometry. What expires is what it points to: shortened links, hosted redirects and domains all have lifespans. A direct URL on a domain you keep renewed works indefinitely.

Can a QR code be repaired without reprinting?

Only destination faults. If the code points at a path on a domain you control, fixing the page or adding a redirect heals every printed copy instantly. Image and data faults require regenerating and reprinting.