Fix FirebaseApp with Name [DEFAULT] Already Exists

When initializing Firebase, you may see:

FirebaseApp with name [DEFAULT] already exists

Flutter may report:

[core/duplicate-app]
A Firebase App named "[DEFAULT]" already exists

The app is attempting to create another FirebaseApp with a name that is already registered.

Initialization versus retrieval

Create a FirebaseApp

Android:

FirebaseApp.initializeApp(context, options)

Flutter:

await Firebase.initializeApp(
  options: DefaultFirebaseOptions.currentPlatform,
);

Retrieve an existing FirebaseApp

Android:

FirebaseApp.getInstance()

Flutter:

final app = Firebase.app();

When you only need the existing default app, retrieve it instead of initializing it again.

Android cause 1: Automatic and manual initialization are both enabled

In a standard Android app, FirebaseInitProvider initializes [DEFAULT] automatically.

Manually initializing it again from Application can create a duplicate:

class MyApplication : Application() {
    override fun onCreate() {
        super.onCreate()
        FirebaseApp.initializeApp(this, options)
    }
}

For a standard setup, remove the manual initialization and retrieve the existing app:

val app = FirebaseApp.getInstance()

Android cause 2: Initialization exists in multiple places

Search the whole project for:

FirebaseApp.initializeApp
FirebaseOptions.Builder
[DEFAULT]

Check locations such as:

• Application
• Activity
• Service
• ContentProvider
• Dependency-injection modules
• Startup managers
• Flavor-specific source sets

Assign responsibility for creating each FirebaseApp to one startup path.

Flutter cause 1: Firebase is initialized outside main as well

Example:

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp(
    options: DefaultFirebaseOptions.currentPlatform,
  );
  await FirebaseService.initialize();
  runApp(const MyApp());
}

If FirebaseService.initialize() performs the same Firebase.initializeApp() call, the second call can fail.

Service classes should use existing instances:

class FirebaseService {
  FirebaseApp get app => Firebase.app();
  FirebaseAuth get auth => FirebaseAuth.instance;
}

Flutter cause 2: Initialization is inside a Widget build method

build() can run many times.

Avoid:

Widget build(BuildContext context) {
  Firebase.initializeApp(
    options: DefaultFirebaseOptions.currentPlatform,
  );
  return const HomePage();
}

Place initialization in main() or another startup function that runs once.

Flutter cause 3: A Provider is recreated

Initialization inside a Provider or Riverpod factory may run again when its lifecycle recreates the provider.

Initialize during startup and pass the created app into the provider layer:

final app = await Firebase.initializeApp(
  options: DefaultFirebaseOptions.currentPlatform,
);

runApp(
  ProviderScope(
    overrides: [firebaseAppProvider.overrideWithValue(app)],
    child: const MyApp(),
  ),
);

Cause 4: Multiple main files and a shared bootstrap both initialize

A project may contain:

main_development.dart
main_production.dart
bootstrap.dart

Check whether each main file initializes Firebase before calling a shared bootstrap that initializes it again.

A clearer design gives the bootstrap function sole responsibility:

Future<void> bootstrap(FirebaseOptions options) async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp(options: options);
  runApp(const MyApp());
}

Cause 5: Two Firebase projects use the same app name

Both calls below use the default name because neither specifies name:

await Firebase.initializeApp(
  options: primaryOptions,
);

await Firebase.initializeApp(
  options: secondaryOptions,
);

Give the second app a unique name:

final secondary = await Firebase.initializeApp(
  name: 'secondary',
  options: secondaryOptions,
);

Then obtain services from that named app:

final auth = FirebaseAuth.instanceFor(app: secondary);

A named app is useful only when the application intentionally connects to more than one Firebase project. Do not create extra apps merely to hide a duplicate default initialization.

Cause 6: Old manual Flutter Web initialization remains

Check whether web/index.html still initializes Firebase in JavaScript in addition to Dart:

<script>
  firebase.initializeApp(firebaseConfig);
</script>

With a current FlutterFire setup, Firebase initialization should normally be owned by the Dart startup path.

When it happens only after Hot Restart

Hot Restart reruns Dart startup code. A Full Restart may temporarily clear the state, but multiple initialization paths can make the error return.

Check all of the following:

• Search every initializeApp call
• Review native Android initialization
• Review manual JavaScript initialization on web
• Confirm that different options are not assigned to the same app name

A restart is not a permanent fix for duplicate ownership of initialization.

When it happens in tests

Tests may create the same named app repeatedly.

Use a dedicated name and delete it after the test suite:

late FirebaseApp testApp;

setUpAll(() async {
  testApp = await Firebase.initializeApp(
    name: 'test-app',
    options: testOptions,
  );
});

tearDownAll(() async {
  await testApp.delete();
});

Avoid using the production [DEFAULT] app as disposable test state.

Inspect registered apps

Android:

FirebaseApp.getApps(context).forEach {
    Log.d("Firebase", "${it.name}: ${it.options.projectId}")
}

Flutter:

for (final app in Firebase.apps) {
  debugPrint('${app.name}: ${app.options.projectId}');
}

After confirming that an app with the required name exists, replace creation calls with retrieval where appropriate.

Do not catch and ignore the error

Avoid:

try {
  await Firebase.initializeApp();
} catch (_) {}

This also hides unrelated configuration and network errors. Identify the duplicate initialization path instead.

Summary

The basic fix for duplicate-app is:

1. Search every initializeApp call
2. Do not combine Android automatic and manual default initialization
3. Initialize once in Flutter main() or a single bootstrap function
4. Do not initialize from rebuildable Widgets or Providers
5. Give additional FirebaseApp instances unique names
6. Retrieve existing apps with getInstance() or Firebase.app()

When [DEFAULT] does not exist instead, see Fix Default FirebaseApp Is Not Initialized.