Firebase Crashlytics Skill

This skill defines how to correctly use Firebase Crashlytics in Flutter applications.

When to Use

Use this skill when:

• Implementing crash reporting in a Flutter project.
• Capturing fatal errors, non-fatal exceptions, and async/isolate errors.
• Customizing crash reports with keys, logs, and user identifiers.
• Configuring opt-in data collection or disabling reporting in debug builds.
• Uploading symbol files for obfuscated builds.

1. Setup and Configuration

flutter pub add firebase_crashlytics
flutter pub add firebase_analytics  # enables breadcrumb logs for better crash context

Run flutterfire configure to update the Firebase configuration and add the required Crashlytics Gradle plugin for Android.

dart
import 'package:firebase_crashlytics/firebase_crashlytics.dart';

Obfuscated code:

• For apps built with --split-debug-info and/or --obfuscate, upload symbol files for readable stack traces.
• iOS: Flutter 3.12.0+ and Crashlytics Flutter plugin 3.3.4+ handle symbol upload automatically.
• Android: Use Firebase CLI (v11.9.0+) to upload Flutter debug symbols:

bash
firebase crashlytics:symbols:upload --app=FIREBASE_APP_ID PATH/TO/symbols

2. Error Handling

Configure comprehensive error capture in main() to catch errors from all sources:

Fatal Flutter errors:

dart
void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();

  // Pass all uncaught fatal errors from the framework to Crashlytics
  FlutterError.onError = FirebaseCrashlytics.instance.recordFlutterFatalError;

  // Catch async errors not handled by the Flutter framework
  PlatformDispatcher.instance.onError = (error, stack) {
    FirebaseCrashlytics.instance.recordError(error, stack, fatal: true);
    return true;
  };

  runApp(MyApp());
}

Non-fatal Flutter errors: use recordFlutterError instead of recordFlutterFatalError.

Isolate errors:

dart
Isolate.current.addErrorListener(RawReceivePort((pair) async {
  final List<dynamic> errorAndStacktrace = pair;
  await FirebaseCrashlytics.instance.recordError(
    errorAndStacktrace.first,
    errorAndStacktrace.last,
    fatal: true,
  );
}).sendPort);

Caught exceptions (non-fatal):

dart
await FirebaseCrashlytics.instance.recordError(
  error,
  stackTrace,
  reason: 'a non-fatal error',
  information: ['further diagnostic information about the error', 'version 2.0'],
);

• Crashlytics only stores the most recent 8 non-fatal exceptions per session — older ones are discarded.

3. Crash Report Customization

Custom keys (max 64 key/value pairs, up to 1 kB each):

dart
FirebaseCrashlytics.instance.setCustomKey('str_key', 'hello');
FirebaseCrashlytics.instance.setCustomKey('bool_key', true);
FirebaseCrashlytics.instance.setCustomKey('int_key', 1);

Custom log messages (limit: 64 kB per session):

dart
FirebaseCrashlytics.instance.log("User tapped on payment button");

User identifier:

dart
FirebaseCrashlytics.instance.setUserIdentifier("user-123");
// Clear by setting to blank string
FirebaseCrashlytics.instance.setUserIdentifier("");

• Avoid putting unique values (user IDs, timestamps) directly in exception messages — use custom keys instead.

4. Performance and Optimization

• Crashlytics processes exceptions on a dedicated background thread to minimize performance impact.
• Fatal reports are sent in real-time without requiring an app restart.
• Non-fatal reports are written to disk and sent with the next fatal report or on app restart.
• Use breadcrumb logs (requires Firebase Analytics) to understand user actions leading up to a crash.

Disable Crashlytics in debug builds:

dart
if (kReleaseMode) {
  await FirebaseCrashlytics.instance.setCrashlyticsCollectionEnabled(true);
} else {
  await FirebaseCrashlytics.instance.setCrashlyticsCollectionEnabled(false);
}

5. Testing and Debugging

Force a test crash to verify the setup:

dart
FirebaseCrashlytics.instance.crash();

Verification workflow:

1. Build and run the app in release mode.
2. Trigger the test crash.
3. Reopen the app so the crash report is uploaded.
4. Check the Firebase Console Crashlytics dashboard within 5 minutes.
5. Verify that custom keys, logs, and user identifiers appear on the crash report.

• Verify stack traces are properly symbolicated when using code obfuscation.

6. Opt-in Reporting

By default, Crashlytics automatically collects crash reports for all users.

To give users control over data collection:

• Disable automatic reporting and enable it only via setCrashlyticsCollectionEnabled(true) when users opt in.
• The override value persists across all subsequent app launches.
• To opt a user out, pass false — this applies from the next app launch.
• When disabled, crash info is stored locally; if later enabled, locally stored crashes are sent to Crashlytics.

References

• Firebase Crashlytics Flutter documentation
• Customize crash reports