What Is a Deep Link? Universal Links, Android App Links and Testing Basics
May 28, 2026
Author: Shusaku Yosa
A deep link points directly to specific content on the web or in an app. Mobile implementations include custom URL schemes, iOS Universal Links and Android App Links. A reliable journey also needs a plan for people without the app and those who must sign in. This guide compares the mechanisms and gives a practical testing workflow.
Deep links point to specific content on the web or in an app
A link to a particular web product page rather than a homepage is a deep link in the broader sense. In a mobile app, the term often refers to opening a particular product, booking or content screen. Deep links are not the opposite of hyperlinks; the term emphasizes a specific destination.
Tapping a link and reaching the intended screen are separate stages. Installation, browser, OS, user choices and authentication state affect the result. Linking can reduce navigation effort, but its presence alone does not establish an increase in purchases or registrations.
Custom schemes versus Universal Links and Android App Links
The methods differ in both URL form and how the website and application are associated. The paths below are illustrative, not live destinations.
Mechanism | URL form | Association | Uninstalled journey or extra requirement |
|---|---|---|---|
Custom URL scheme | An application scheme such as exampleapp with a path such as /items/42 | The app handles that scheme | A working web fallback is not automatic |
Universal Links | An HTTPS URL with a path such as /items/42 | iOS Associated Domains and AASA | Provide useful web content and test invocation conditions |
Android App Links | An HTTPS URL with a path such as /items/42 | Verified website association using Digital Asset Links | Check verification state and device settings |
Deferred deep linking | A design that carries selected context through installation | Depends on the handoff method | Installation and context restoration need separate implementation and tests |
Use Apple’s Universal Links guidance and the Android App Links documentation for platform-specific requirements. A custom scheme does not establish the same verified HTTPS-domain association.
Verified association and a usable web fallback
On iOS, configure the app’s Associated Domains capability and the website’s apple-app-site-association, or AASA, information. Android uses corresponding application settings and Digital Asset Links information on the website. An Android signing-certificate fingerprint is not the same thing as a TLS certificate for web transport.
A valid association does not guarantee that every tap opens the app. Apple describes cases where a same-domain link in Safari stays in Safari. Use the Universal Links debugging guidance to investigate the domain, path, app settings and invocation context.
Provide a usable web alternative for people who cannot or do not want to install the app. A fallback should preserve access to relevant information or a task where possible, rather than merely replacing a failed launch with an install prompt.
Deferred deep linking needs a separate handoff design
Deferred deep linking restores selected content after a person installs the app. It requires a separate context handoff and restoration design. Ordinary Universal Links or App Links alone do not guarantee that the original product or campaign context survives installation.
Decide which context to retain, how long it remains valid and what to show when restoration is unavailable. Test store navigation separately from first-launch restoration, accounting for OS, store and service support. Firebase Dynamic Links is not a new implementation option: its official FAQ records the service shutdown on 25 August 2025.
Test installed, uninstalled and signed-out journeys
Use these eight baseline cases as a test register. For each, record the expected design, the actual opened surface, post-login destination, available web fallback and any defect. This is a checklist of conditions, not a guarantee of identical behavior.
OS | App installed | Signed in | Main check |
|---|---|---|---|
iOS | Yes | Yes | Correct screen and content ID |
iOS | Yes | No | Intended destination after authentication |
iOS | No | Yes | Usable web alternative and install option |
iOS | No | No | Web authentication, fallback and restoration tested separately |
Android | Yes | Yes | Verification state and correct screen |
Android | Yes | No | Destination after login and authorization |
Android | No | Yes | Complete the purpose through a web alternative |
Android | No | No | Separate fallback, login and post-install checks |
Web and app authentication may be independent, so specify which session is signed in. Add browser or source context, including same-domain Safari navigation, email and in-app browsers, plus OS and application versions. Test nonexistent, removed and unauthorized content IDs as well as the normal case.
Secure destinations and measure outcomes without personal data in URLs
Website–app association establishes a relationship between the domain and application; it does not authorize a person to view private content. The destination must still enforce authentication and authorization. Changing an identifier in a URL must not grant access to another user’s information.
- Define the destination and a usable web alternative.
- Prepare the required domain association separately for each OS.
- Allow only intended paths and parameters; reject unexpected redirect destinations.
- Check authentication, authorization and invalid identifiers at the destination.
- Test post-login return paths on devices and post-install restoration where required.
- Measure link actions, screen arrivals and accepted outcomes as separate stages.
Do not place email addresses or authentication tokens in analytics URLs. Click counts are not registrations. Review consent, web-to-app measurement scope, duplicates and the success definition before reporting outcomes. Begin with one representative destination and document the conditions in which it works and the fallback offered elsewhere.
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