# Design Mobile Deep Linking and Universal Links

Source: https://www.techinterview.org/post/3233475135/design-mobile-deep-linking-universal-links/
Updated: 2026-06-30 · techinterview.org

Deep linking — the ability to open a specific screen in your app from a URL — is fundamental to mobile UX. A link in an email, a Google search result, a friend's text message: each should open the right screen with the right context. The interview tests whether you understand the platform mechanics, the deferred-link case, and the routing architecture.

## Three types of links

### Custom URL schemes

`myapp://product/123`. Original mechanism. Problem: any app can register the scheme, leading to conflicts.

### Universal Links (iOS)

HTTPS URLs your app can intercept. Apple verifies via a JSON file at `/.well-known/apple-app-site-association`. If the app is installed, link opens in app; if not, in Safari.

### App Links (Android)

Same pattern: HTTPS URLs verified via `/.well-known/assetlinks.json`. Android opens the app if installed.

## Why universal/app links over custom schemes

- Same URL works on web and mobile

- No "app not installed" failure — gracefully falls back to web

- Verified ownership prevents conflicts

- Better SEO (real URLs)

## Routing inside the app

When a deep link opens the app:

- Parse the URL into a route + parameters

- Determine if the user is signed in

- Route to the destination screen with the parameters

- Optionally fetch additional data based on the link

## Deferred deep links

Scenario: user clicks a marketing link, app is not installed, they install from the app store, and you want them to land on the original destination after install.

Implementation:

- Marketing URL captures campaign data (UTM, link target)

- Sends user to App Store / Play Store

- After install, on first launch, app fetches the deferred link data from a service (Branch, AppsFlyer, Adjust, or a homegrown server)

- App routes to the original destination

Tools: Branch, AppsFlyer, Adjust handle the cross-store attribution. Apple SKAdNetwork (iOS) and Android Install Referrer also support similar patterns.

## Authentication-protected deep links

If the deep link points to authenticated content:

- App checks auth state

- If signed in, route to destination

- If not, show login screen

- After login, route to original destination

## Sharing from your app

The "share" button generates a universal link. Best practices:

- The link works on web (so non-app users can see content)

- The link gracefully promotes the app (smart banner on web)

- Track link clicks for engagement analytics

## Server-side validation

Both platforms verify ownership via files at well-known paths:

- iOS: `https://yourdomain.com/.well-known/apple-app-site-association`

- Android: `https://yourdomain.com/.well-known/assetlinks.json`

These must be served over HTTPS with proper Content-Type. Typos here cause silent failures.

## Routing architecture

Modern app routing:

- iOS: NSURLSession with universal link handling; SwiftUI deep-link API

- Android: Navigation Component with deep-link support; intent filters in manifest

- React Native: react-navigation with linking config

- Flutter: go_router, Flutter's built-in deep-link API

## Common bugs

- Universal links not working in Slack/Notes apps (some apps strip the universal-link behavior)

- Routing fails silently when the user is in a sign-up flow

- Links from email open in Safari instead of the app (iOS sometimes does this for "long-press" cases)

- Deferred links failing because the attribution service never fired

## Frequently Asked Questions

### Should I use Branch / AppsFlyer or build my own attribution?

For most apps, use a vendor. Building your own deferred-link attribution well takes engineering effort that vendors have already done.

### Do universal links work for QR codes?

Yes. The QR encodes a URL; the system detects universal links and opens the app if installed.

### What about iMessage and other messaging apps?

Some messaging apps render universal links as native cards (preview metadata). Provide good Open Graph tags for these.