Understanding Deep Links

Deep links allow you to take users directly to specific content within your mobile app from external sources like websites, emails, or other apps.

Types of Deep Links

1. Custom URL Schemes

The simplest form of deep linking, using a custom protocol:

• Format: myapp://path/to/content
• Pros: Easy to implement, works offline
• Cons: Not secure, prompts user, no fallback
• Use Case: App-to-app communication

2. iOS Universal Links

Apple's solution for seamless web-to-app deep linking:

• Format: https://example.com/path
• Pros: No prompts, fallback to web, secure
• Cons: Requires server configuration
• Use Case: Professional apps with web presence

3. Android App Links

Google's verified deep link solution:

• Format: https://example.com/path
• Pros: Verified, no disambiguation, secure
• Cons: Requires domain verification
• Use Case: Android apps with web equivalents

Universal Links (iOS) Setup

Requirements

• iOS 9.0 or later
• HTTPS domain you control
• Apple App Site Association (AASA) file
• Associated Domains entitlement

AASA File Format

{
    "applinks": {
        "apps": [],
        "details": [
            {
                "appID": "TEAMID.bundle.id",
                "paths": [
                    "/products/*",
                    "/user/*/profile",
                    "NOT /admin/*"
                ]
            }
        ]
    },
    "webcredentials": {
        "apps": ["TEAMID.bundle.id"]
    }
}

Path Patterns

• /path: Exact match
• /path/*: Wildcard match
• NOT /path: Exclude path
• ?*: Match query strings

Android App Links Setup

Requirements

• Android 6.0 (API 23) or later
• HTTPS domain you control
• Digital Asset Links file
• Intent filter with autoVerify

Getting SHA256 Fingerprint

# Debug keystore
keytool -list -v -keystore ~/.android/debug.keystore -alias androiddebugkey -storepass android -keypass android

# Release keystore
keytool -list -v -keystore my-release-key.keystore

Testing Verification

# Check verification status
adb shell dumpsys package domain-preferred-apps

# Test statement list
https://digitalassetlinks.googleapis.com/v1/statements:list?source.web.site=https://example.com

Best Practices

URL Structure

• Keep URLs simple: Easy to type and remember
• Use meaningful paths: /product/123 not /p/123
• Support variations: Handle with and without trailing slashes
• Include IDs: Make links shareable and specific

Fallback Handling

• Always provide web fallback for universal/app links
• Show install prompt on web if app not installed
• Use smart banners (iOS) or app banners (Android)
• Track conversion from web to app install

User Experience

• Deep link to specific content, not just home screen
• Maintain context when switching from web to app
• Handle authentication gracefully
• Show loading states during deep link resolution

Common Issues

iOS Universal Links Not Working

• AASA file not accessible (check HTTPS, redirects)
• Wrong Team ID in AASA file
• Associated Domains not configured correctly
• Links clicked in same domain (long-press to open in app)
• Cache issues (uninstall/reinstall app)

Android App Links Not Verifying

• SHA256 fingerprint mismatch
• assetlinks.json not accessible
• Wrong package name in manifest
• autoVerify attribute missing
• Intent filter order matters

Debugging Deep Links

iOS

# Test AASA file
curl -v https://example.com/.well-known/apple-app-site-association

# Validate AASA
https://search.developer.apple.com/appsearch-validation-tool/

# Check device logs
Console.app → filter for "swcd"

Android

# Test assetlinks.json
curl https://example.com/.well-known/assetlinks.json

# Verify App Links
adb shell pm verify-app-links --re-verify com.example.app

# Check logs
adb logcat | grep -i "IntentFilter"

Advanced Techniques

Deferred Deep Linking

Take users to specific content even on first app install:

• Store link data before app store redirect
• Retrieve and apply link after install
• Use services like Branch, Firebase Dynamic Links

Contextual Deep Links

Pass additional context with deep links:

• Campaign tracking parameters
• Referral information
• User preferences
• Authentication tokens (carefully!)