miji.beA deep link is a technique that takes users directly from a web browser, email, social media, and so on to a specific screen of a mobile app. While a regular link opens the app's top screen, a deep link can specify and open any screen within the app, such as a product detail page, a specific article, or a user profile. Campaigns that use deep links can have a higher conversion rate than regular links. The reason for this difference is that the number of steps from when the user taps the link until reaching the content is reduced. A regular link requires 4 steps, "open in the browser → launch the app → top screen → look for the target screen", while a deep link completes in 1 step, "tap → target screen".
There are 3 main methods for deep links. The first is the URI scheme (Custom URL Scheme). It specifies the destination using a scheme unique to the app, such as "myapp://product/12345". It is a long-established method and easy to implement, but it has the drawback that an error occurs when the app is not installed. In addition, when different apps register the same scheme, a scheme collision occurs, and there is also a risk that an unintended app will launch. The second is iOS Universal Links. It is a method Apple introduced in iOS 9, and it associates a regular HTTPS URL (example: https://example.com/product/12345) with a specific screen of the app. It comes standard with a fallback behavior: if the app is installed, the app opens, and if it is not installed, the page is displayed in the web browser. The third is Android App Links. It is a method introduced in Android 6.0, and like Universal Links, it associates an HTTPS URL with the app.
Let us dig into the technical background of why Universal Links and App Links are better than URI schemes. Because URI schemes are not guaranteed to be unique across apps, there is a risk that a malicious app will register the same scheme and use it for phishing attacks. Universal Links and App Links have a mechanism that verifies ownership of the HTTPS domain, so it is difficult for anyone other than the domain owner to hijack the links. This verification is achieved by the OS automatically fetching / verifying a configuration file (AASA or assetlinks.json) placed on the web server. When the app is installed, iOS downloads the AASA file via Apple's CDN and caches the association between the domain and the app. When verifying App Links, Android fetches the domain's assetlinks.json directly and matches the package name and the SHA-256 fingerprint.
Combining short URLs with deep links is a technique used in marketing. By converting a long deep link URL into a short URL, you can share it concisely in social media posts and emails. For example, if you shorten the deep link to a product page in an e-commerce app, "https://example.com/app/product/12345?utm_source=email&utm_campaign=summer-sale", to "brand.co/summer-item", it looks cleaner and an improvement in the click-through rate can be expected. Users who arrive via deep links may spend longer in the app and go on to make a purchase. Behind this difference, it is thought that deep links reduce drop-off along the way by directly connecting the user's "intent" with the "destination".
A deferred deep link is an advanced technique that also handles users who have not installed the app. If the app is not installed when the user clicks the link, the user is first guided to the App Store or Google Play, and after the app installation is complete, the originally intended destination screen opens automatically. Attribution tools such as Branch, AppsFlyer, and Adjust provide this feature. Technically, device information at the time of the click (IP address, User-Agent, screen resolution, etc.) is recorded on the server, and by matching the same device information when the app is launched for the first time, the click before installation is linked to the launch after installation.
Here is an overview of the technical implementation. To set up Universal Links, as described in Apple's documentation (as of October 2026), you place an apple-app-site-association (AASA) file in the .well-known directory of the web server and describe the app's Bundle ID and the corresponding URL paths in JSON format. Example of an AASA file: {"applinks":{"apps":[],"details":[{"appID":"TEAMID.com.example.app","paths":["/myapp/items/*","/myapp/posts/*"]}]}}. For App Links, you place an assetlinks.json file in the .well-known directory and describe the app's package name and SHA-256 fingerprint. In both cases HTTPS is required, and the AASA file must be served without redirects.
With deep links that go through a URL shortener, you need to pay attention to redirect behavior. This is a point where implementations tend to stumble. With Universal Links and App Links, the transition to the app may not occur when going through an HTTP redirect (301/302). This is because the OS looks up AASA/assetlinks.json on the domain of the redirect source, not the redirect destination. There are 2 ways to avoid this problem. The first is to configure deep link support on the URL shortener side. Some services provide a proxy feature for the AASA file. The second is to return an HTML page instead of a 302 redirect on the server side and make the transition with JavaScript's window.location. In the latter case, the OS can correctly refer to the AASA file of the destination domain. However, because a JavaScript redirect involves loading a page, there is a trade-off: the transition is slower compared with a server-side redirect.
As drawbacks, implementing and operating deep links involves several challenges. First, you need to support different technical specifications on iOS and Android, which increases development costs. Second, specifications may change with OS version upgrades, so continuous maintenance is required. From iOS 14 onward, AASA files are delivered via Apple's CDN, and it can take time for updates to reach devices. Third, you need to properly design fallback handling for cases where the user has uninstalled the app or the app version is old. Fourth, due to stronger privacy regulations (such as the ATT framework on iOS), the attribution accuracy of deferred deep links tends to decline. According to Apple's documentation (as of October 2026), apps cannot track users without obtaining their permission through ATT, which makes user-level tracking difficult. Fifth, building a test environment is complex. Testing on real devices is essential to verify how deep links behave, and the behavior of Universal Links is hard to reproduce in the simulator.
Deep links are a technique that helps improve the user experience of mobile apps and the conversion rate of marketing campaigns. When combined with short URLs, it is thought that the transition to the app also becomes smoother while keeping the links manageable and trackable.