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Glossary

Deep link

A deep link is a URL that opens a specific screen inside an app rather than a website. In QR codes they appear as custom schemes like upi://pay or as universal links — normal https URLs that the OS routes into an installed app and that fall back to the web when it is absent.

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Two kinds, one crucial difference

Custom schemes (myapp://…, upi://pay?…, tg://resolve?…) go straight to the app — and go nowhere when the app is missing. The scan either errors or silently does nothing, and there is no page to explain what should have happened.

Universal links (iOS) / App Links (Android) are ordinary https:// URLs that the app's developer has verified for their domain. Installed app → the link opens in-app; not installed → the same URL loads in the browser. This built-in fallback is why https://wa.me/447700900123 beats whatsapp://send?phone=… on a printed WhatsApp code, and why UseQR's typed generators emit the https form wherever one exists.

The main exception is payments: UPI codes use the bare upi://pay scheme by design, because the ecosystem guarantees a handler and app choice is the point.

  • Prefer the https:// form whenever the platform offers one; the paper fallback matters more than the app-open elegance.
  • For "download our app", encode a store link or a smart routing page — see app download codes and device-dependent codes.
  • Some in-app scanners refuse unknown custom schemes outright; always test the payload on both platforms before printing.

FAQ

Can a QR code open an app directly?

Yes — encode a deep link. A universal/App Link (https URL) opens the installed app and falls back to the browser otherwise; a custom scheme like myapp:// opens the app but fails with nothing to show when it is not installed.

Why does my app QR code do nothing on some phones?

Almost always a custom-scheme payload on a phone without the app, or an in-app scanner that blocks unknown schemes. Switch to the https universal-link form so every phone at least reaches a web page.

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