App Clip

Definition

An App Clip is a lightweight portion of an iOS app that a user can launch from a URL, code, or NFC tag without installing the full app from the App Store.

For deep linking it is a strange and useful case: the App Clip is launched by a URL, so every invocation is a deep link by definition — and because it runs without an install, it sits in the middle of the fallback chain between a web page and a full app. It also has its own attribution rules, which almost no glossary covers and which quietly break assumptions carried over from full-app measurement.

How an App Clip is invoked

Every launch starts from a URL — the invocation URL — even when the user scanned a code or tapped a tag. That URL is registered as an App Clip Experience in App Store Connect and authorised by your domain's AASA file.

{
  "appclips": {
    "apps": ["A1B2C3D4E5.com.example.shop.Clip"]
  },
  "applinks": {
    "details": [
      {
        "appIDs": ["A1B2C3D4E5.com.example.shop"],
        "components": [{ "/": "/table/*" }]
      }
    ]
  }
}

Reading the invocation URL

The URL arrives the same way a Universal Link does — as an NSUserActivity — which means the routing code you already have mostly works. What differs is that for an App Clip this is the *only* entry point.

@main
struct ShopClip: App {
    var body: some Scene {
        WindowGroup {
            ClipRootView()
                .onContinueUserActivity(NSUserActivityTypeBrowsingWeb) { activity in
                    guard let url = activity.webpageURL else { return }
                    // https://example.com/table/42?promo=spring
                    Router.shared.handle(url)

                    // Persist for the full app to pick up after an upgrade
                    if let shared = UserDefaults(suiteName: "group.com.example.shop") {
                        shared.set(url.absoluteString, forKey: "clipInvocationURL")
                    }
                }
        }
    }
}

Local testing does not require App Store Connect: set the _XCAppClipURL environment variable in the App Clip scheme and Xcode passes it as the invocation URL on launch.

# Xcode > Edit Scheme > Run > Arguments > Environment Variables
_XCAppClipURL = https://example.com/table/42?promo=spring

# Or on a booted simulator
xcrun simctl openurl booted "https://example.com/table/42?promo=spring"

# Confirm the appclips key is present in the served file
curl -sS https://example.com/.well-known/apple-app-site-association | \
  python3 -m json.tool | grep -A 3 appclips

The constraints

The size budget is the constraint that shapes the build. It applies to the uncompressed clip, so large frameworks, unoptimised assets and an SDK pulled in for one call are the usual reasons a clip does not fit. Attribution SDKs are worth measuring before adopting: an integration whose only job in the clip is to read a URL you already have is rarely worth the budget.

Attribution across the upgrade

The valuable event is not the invocation; it is the user who then installs the full app. The chain between them is deterministic, but only if you build it.

1. The clip receives the invocation URL, including whatever campaign parameters your link carried.
2. It writes what matters into a shared App Group container — the clip and the full app must declare the same group.
3. The user is offered the full app, ideally through SKOverlay.AppClipConfiguration rather than a link out.
4. After install, the full app reads the shared container on first launch and recovers the original URL.
5. The install is attributed to the original campaign with no probabilistic matching and no device identifier involved.