Firebase Crashlytics

Firebase Crashlytics Skill

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

When to Use

Use this skill when:

• Setting up Crashlytics in a Flutter project.
• Configuring fatal and non-fatal error handling.
• Customizing crash reports with keys, logs, and user identifiers.
• Testing crash reporting or configuring opt-in data collection.

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 your Firebase configuration and add the required Crashlytics Gradle plugin for Android.

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 before reporting crashes:

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

2. Error Handling

Fatal Flutter errors:

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

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

  runApp(MyApp());
}

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

Async errors not caught by the Flutter framework:

PlatformDispatcher.instance.onError = (error, stack) {
  FirebaseCrashlytics.instance.recordError(error, stack, fatal: true);
  return true;
};

Isolate errors:

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):

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):

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):

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

User identifier:

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.
• Crashlytics rate-limits reports from a device to reduce network traffic if necessary.
• Use breadcrumb logs (requires Firebase Analytics) to understand user actions leading up to a crash.

Disable Crashlytics in debug builds:

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

5. Testing and Debugging

Force a test crash to verify your setup:

FirebaseCrashlytics.instance.crash();

• Test both fatal and non-fatal error reporting.
• Verify stack traces are properly symbolicated when using code obfuscation.
• Check that custom keys, logs, and user identifiers are associated with crash reports.
• Monitor the Crashlytics dashboard regularly and set up alerts for new issues or regressions.

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

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