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Using Firebase Crashlytics

Getting started#

Enable Firebase Crashlytics in the Firebase console.

Enable in the console
Enable in the console

Until an error has been reported, you will see this screen.

Crashlytics init screen
Crashlytics init screen

To start using Firebase Crashlytics within your project, import it at the top of your project files:

import 'package:firebase_crashlytics/firebase_crashlytics.dart';

Run an example, such as...

// Initialize Firebase.
await Firebase.initializeApp();
// Elsewhere in your code

This will crash the currently running application. You will then need to manually re-run your application on your emulator for Crashlytics to submit the crash report to the Firebase Console.

Sending reports to Crashlytics#

To send report data to Crashlytics, the application must be restarted. Crashlytics automatically sends any crash reports to Firebase the next time the application is launched.

Toggle Crashlytics collection#

Call the setCrashlyticsCollectionEnabled method to toggle Crashlytics collection status.

For example to ensure it is disabled when your app is in debug mode you can do the following:

import 'package:flutter/foundation.dart' show kDebugMode;
// ...
if (kDebugMode) {
// Force disable Crashlytics collection while doing every day development.
// Temporarily toggle this to true if you want to test crash reporting in your app.
await FirebaseCrashlytics.instance
} else {
// Handle Crashlytics enabled status when not in Debug,
// e.g. allow your users to opt-in to crash reporting.

You can additionally read the current collection enabled status:

if (FirebaseCrashlytics.instance.isCrashlyticsCollectionEnabled) {
// Collection is enabled.

Forcing a crash#

You don't have to wait for a crash to know that Crashlytics is working. To force a crash, call the crash method:


Your app should exit immediately after calling this method. After opening your app again after the crash Firebase Crashlytics will upload the crash report to the Firebase Console.

The error will be shown on the Firebase Crashlytics dashboard as an instance of FirebaseCrashlyticsTestCrash, with a message of This is a test crash caused by calling .crash() in Dart.

Crash types#

Fatal crash#

If you would like to record a fatal error, you may pass in a fatal argument as true. The crash report will appear in your Crashlytics dashboard with the event type Crash, the event summary stack trace will also be referenced as a Fatal Exception.

await FirebaseCrashlytics.instance.recordError(
reason: 'a fatal error',
// Pass in 'fatal' argument
fatal: true

Non-Fatal crash#

By default non-fatal errors are recorded. The crash report will appear in your Crashlytics dashboard with the event type Non-fatal, the event summary stack trace will also be referenced as a Non-fatal Exception.

await FirebaseCrashlytics.instance.recordError(
reason: 'a non-fatal error'

Add custom keys#

To associate key/value pairs with your crash reports, you can use the setCustomKey method

// Set a key to a string.
FirebaseCrashlytics.instance.setCustomKey('str_key', 'hello');
// Set a key to a boolean.
FirebaseCrashlytics.instance.setCustomKey("bool_key", true);
// Set a key to an int.
FirebaseCrashlytics.instance.setCustomKey("int_key", 1);
// Set a key to a long.
FirebaseCrashlytics.instance.setCustomKey("int_key", 1L);
// Set a key to a float.
FirebaseCrashlytics.instance.setCustomKey("float_key", 1.0f);
// Set a key to a double.
FirebaseCrashlytics.instance.setCustomKey("double_key", 1.0);

This accepts a maximum of 64 key/value pairs. New keys beyond that limit are ignored. Keys or values that exceed 1024 characters are truncated.

Add custom log messages#

To add custom Crashlytics log messages to your app, use the log method

FirebaseCrashlytics.instance.log("Higgs-Boson detected! Bailing out");

Set user identifiers#

To add user IDs to your reports, assign each user with a unique ID. This can be an ID number, token or hashed value:


To reset a user ID (e.g. when a user logs out), set the user ID to an empty string.

Handling uncaught errors#

By overriding FlutterError.onError with FirebaseCrashlytics.instance.recordFlutterError, it will automatically catch all errors that are thrown within the Flutter framework.

void main() async {
await Firebase.initializeApp();
// Pass all uncaught errors from the framework to Crashlytics.
FlutterError.onError = FirebaseCrashlytics.instance.recordFlutterError;

Zoned Errors#

Not all errors are caught by Flutter. Sometimes, errors are instead caught by Zones.
A common case were FlutterError would not be enough is when an exception happen inside the onPressed of a button:

onPressed: () {
throw Error();

To catch such errors, you can use runZonedGuarded like do:

void main() async {
runZonedGuarded<Future<void>>(() async {
await Firebase.initializeApp();
// The following lines are the same as previously explained in "Handling uncaught errors"
FlutterError.onError = FirebaseCrashlytics.instance.recordFlutterError;
}, (error, stack) => FirebaseCrashlytics.instance.recordError(error, stack));

Note that you must call WidgetsFlutterBinding.ensureInitialized() inside runZonedGuarded. Error handling wouldn’t work if WidgetsFlutterBinding.ensureInitialized() was called from the outside.

Errors outside of Flutter#

To catch errors that happen outside of the Flutter context, install an error listener on the current Isolate:

Isolate.current.addErrorListener(RawReceivePort((pair) async {
final List<dynamic> errorAndStacktrace = pair;
await FirebaseCrashlytics.instance.recordError(

Enable opt-in reporting#

By default, Crashlytics will automatically collect crash reports for all your app's users. To give users more control over the data they send, you can enable opt-in reporting by disabling automatic collection and initializing Crashlytics only for selected users:

  1. Turn off automatic collection natively:

a. Android In the application block of your AndroidManifest.xml file, add a meta-data tags to turn off automatic collection:

android:value="false" />

b. iOS

Add a new key to your Info.plist file.

  • Key: FirebaseCrashlyticsCollectionEnabled
  • Value: false
  1. Enable collection for select users by calling the Crashlytics data collection override at runtime. To opt out of automatic crash reporting, pass false as the override value. When set to false, the new value does not apply until the next run of the app.