What is Universal Links?
Universal Links are Apple's standard mechanism for deep linking on iOS. They allow standard HTTPS URLs to seamlessly open content in a native iOS app instead of Safari. Unlike custom URI schemes, Universal Links use your existing web domain, which means the same URL works whether the user has your app installed or not.
When a user taps a Universal Link and has your app installed, iOS opens the app directly and passes the URL for in-app routing. If the app is not installed, the URL opens normally in Safari, where you can show a web version or redirect to the App Store.
How it works
Universal Links rely on a two-part verification system:
1. Apple App Site Association (AASA) file — A JSON file hosted at https://yourdomain.com/.well-known/apple-app-site-association that declares which URL paths your app can handle. Apple's CDN fetches and caches this file when your app is installed.
2. App entitlements — Your iOS app must include an Associated Domains entitlement listing the domains it can open (e.g., applinks:yourdomain.com).
When both are configured correctly, iOS verifies the association at install time. After verification, tapping any matching URL opens your app instead of Safari. This happens at the OS level — no JavaScript redirect or interstitial page is needed.
Why it matters
Universal Links are the recommended deep linking method on iOS because they provide:
- No interstitial dialogs — The app opens instantly without "Open in app?" prompts - Graceful fallback — If the app isn't installed, the URL works as a normal web link - Security — Domain ownership is verified by Apple, preventing link hijacking - No conflicts — Unlike URI schemes, Universal Links can't be claimed by other apps - User trust — Uses standard HTTPS URLs that users recognize and trust
Frequently asked questions
How do I test if my Universal Links are working?
You can use Redirectly's free AASA Validator tool to check your Apple App Site Association file for errors. For on-device testing, long-press a Universal Link in Notes or Messages — if you see "Open in [App Name]", the link is working correctly.
Why are my Universal Links opening in Safari instead of my app?
Common causes include: an invalid or unreachable AASA file, mismatched bundle IDs or team IDs, the Associated Domains entitlement not being configured, or the user having previously chosen to open links in Safari (which can be reset by long-pressing the link).
Do Universal Links work with all iOS versions?
Universal Links were introduced in iOS 9. All modern iOS versions support them. However, the AASA file format was updated in iOS 14 to support more flexible pattern matching with the "details" array format.
Related terms
Apple App Site Association (AASA)
A JSON configuration file hosted on a web domain that tells iOS which URL paths should open in a native app, enabling Universal Links.
Deep Linking
A technique that uses URIs to link directly to a specific screen or piece of content within a mobile app, rather than simply launching the app's home screen.
Android App Links
Android's verified deep linking mechanism that uses Digital Asset Links to associate HTTPS URLs with an app, allowing links to open directly in the app without a disambiguation dialog.
Deferred Deep Linking
A deep linking technique that preserves the intended destination through the app install process, routing users to specific content after they install and open the app for the first time.