Customize your Firebase Crashlytics crash reports

In the Crashlytics dashboard, you can click into an issue and get a detailed event report. You can customize those reports to help you better understand what's happening in your app and the circumstances around events reported to Crashlytics.

  • Automatically get breadcrumb logs if your app uses the Firebase SDK for Google Analytics. These logs give you visibility into user actions leading up to a Crashlytics-collected event in your app.

  • Turn off automatic crash reporting and enable opt-in reporting for your users. Note that, by default, Crashlytics automatically collects crash reports for all your app's users.

Add custom keys

Custom keys help you get the specific state of your app leading up to a crash. You can associate arbitrary key/value pairs with your crash reports, then use the custom keys to search and filter crash reports in the Firebase console.

  • In the Crashlytics dashboard, you can search for issues that match a custom key.
  • When you're reviewing a specific issue in the console, you can view the associated custom keys for each event (Keys subtab) and even filter the events by custom keys (Filter menu at the top of the page).

Use the setCustomValue method to set key/value pairs. For example:


// Set int_key to 100.
Crashlytics.crashlytics().setCustomValue(100, forKey: "int_key")

// Set str_key to "hello".
Crashlytics.crashlytics().setCustomValue("hello", forKey: "str_key")


When setting integers, booleans, or floats, box the value as @(value).

// Set int_key to 100.
[[FIRCrashlytics crashlytics] setCustomValue:@(100) forKey:@"int_key"];

// Set str_key to "hello".
[[FIRCrashlytics crashlytics] setCustomValue:@"hello" forKey:@"str_key"];

You can also modify the value of an existing key by calling the key and setting it to a different value. For example:


Crashlytics.crashlytics().setCustomValue(100, forKey: "int_key")

// Set int_key to 50 from 100.
Crashlytics.crashlytics().setCustomValue(50, forKey: "int_key")


[[FIRCrashlytics crashlytics] setCustomValue:@(100) forKey:@"int_key"];

// Set int_key to 50 from 100.
[[FIRCrashlytics crashlytics] setCustomValue:@(50) forKey:@"int_key"];

Add key/value pairs in bulk by using the setCustomKeysAndValues method with an NSDictionary as the only parameter:


let keysAndValues = [
                 "string key" : "string value",
                 "string key 2" : "string value 2",
                 "boolean key" : true,
                 "boolean key 2" : false,
                 "float key" : 1.01,
                 "float key 2" : 2.02
                ] as [String : Any]



NSDictionary *keysAndValues =
    @{@"string key" : @"string value",
      @"string key 2" : @"string value 2",
      @"boolean key" : @(YES),
      @"boolean key 2" : @(NO),
      @"float key" : @(1.01),
      @"float key 2" : @(2.02)};

[[FIRCrashlytics crashlytics] setCustomKeysAndValues: keysAndValues];

Add custom log messages

To give yourself more context for the events leading up to a crash, you can add custom Crashlytics logs to your app. Crashlytics associates the logs with your crash data and displays them in the Crashlytics page of the Firebase console, under the Logs tab.


Use log() or log(format:, arguments:) to help pinpoint issues. If you want to get a useful log output with messages, the object that you pass to log() must conform to the CustomStringConvertible property. log() returns the description property you define for the object. For example:

Crashlytics.crashlytics().log("Higgs-Boson detected! Bailing out…, \(attributesDict)")

.log(format:, arguments:) formats values returned from calling getVaList(). For example:

Crashlytics.crashlytics().log(format: "%@, %@", arguments: getVaList(["Higgs-Boson detected! Bailing out…", attributesDict]))

For more details on how to use log() or log(format:, arguments:), refer to the Crashlytics reference documentation.


Use log or logWithFormat to help pinpoint issues. Note that if you want to get a useful log output with messages, the object that you pass to either method must override the description instance property. For example:

[[FIRCrashlytics crashlytics] log:@"Simple string message"];

[[FIRCrashlytics crashlytics] logWithFormat:@"Higgs-Boson detected! Bailing out... %@", attributesDict];

[[FIRCrashlytics crashlytics] logWithFormat:@"Logging a variable argument list %@" arguments:va_list_arg];

For more details on how to use log and logWithFormat, refer to the Crashlytics reference documentation.

Set user identifiers

To diagnose an issue, it’s often helpful to know which of your users experienced a given crash. Crashlytics includes a way to anonymously identify users in your crash reports.

To add user IDs to your reports, assign each user a unique identifier in the form of an ID number, token, or hashed value:




[[FIRCrashlytics crashlytics] setUserID:@"123456789"];

If you ever need to clear a user identifier after you set it, reset the value to a blank string. Clearing a user identifier does not remove existing Crashlytics records. If you need to delete records associated with a user ID, contact Firebase support.

Report non-fatal exceptions

In addition to automatically reporting your app’s crashes, Crashlytics lets you record non-fatal exceptions and sends them to you the next time your app launches.

You can record non-fatal exceptions by recording NSError objects with the recordError method. recordError captures the thread’s call stack by calling [NSThread callStackReturnAddresses].


Crashlytics.crashlytics().record(error: error)


[[FIRCrashlytics crashlytics] recordError:error];

When using the recordError method, it's important to understand the NSError structure and how Crashlytics uses the data to group crashes. Incorrect usage of the recordError method can cause unpredictable behavior and may cause Crashlytics to limit reporting of logged errors for your app.

An NSError object has three arguments:

  • domain: String
  • code: Int
  • userInfo: [AnyHashable : Any]? = nil

Unlike fatal crashes, which are grouped via stack trace analysis, logged errors are grouped by domain and code. This is an important distinction between fatal crashes and logged errors. For example:


let userInfo = [
  NSLocalizedDescriptionKey: NSLocalizedString("The request failed.", comment: ""),
  NSLocalizedFailureReasonErrorKey: NSLocalizedString("The response returned a 404.", comment: ""),
  NSLocalizedRecoverySuggestionErrorKey: NSLocalizedString("Does this page exist?", comment: ""),
  "ProductID": "123456",
  "View": "MainView"

let error = NSError.init(domain: NSCocoaErrorDomain,
                         code: -1001,
                         userInfo: userInfo)


NSDictionary *userInfo = @{
  NSLocalizedDescriptionKey: NSLocalizedString(@"The request failed.", nil),
  NSLocalizedFailureReasonErrorKey: NSLocalizedString(@"The response returned a 404.", nil),
  NSLocalizedRecoverySuggestionErrorKey: NSLocalizedString(@"Does this page exist?", nil),
  @"ProductID": @"123456",
  @"View": @"MainView",

NSError *error = [NSError errorWithDomain:NSCocoaErrorDomain

When you log the error above, it creates a new issue that is grouped by NSSomeErrorDomain and -1001. Additional logged errors that use the same domain and code values are grouped under the same issue. Data contained within the userInfo object are converted to key-value pairs and displayed in the keys/logs section within an individual issue.

Logs and custom keys

Just like crash reports, you can embed logs and custom keys to add context to the NSError. However, there is a difference in what logs are attached to crashes versus logged errors. When a crash occurs and the app is relaunched, the logs Crashlytics retrieves from disk are those that were written right up to the time of the crash. When you log an NSError, the app does not immediately terminate. Because Crashlytics only sends the logged error report on the next app launch and must limit the amount of space allocated for logs on disk, it is possible to log enough after an NSError is recorded so that all relevant logs are rotated out by the time Crashlytics sends the report from the device. Keep this balance in mind when logging NSErrors and using logs and custom keys in your app.

Performance considerations

Keep in mind that logging an NSError can be fairly expensive. At the time you make the call, Crashlytics captures the current thread’s call stack using a process called stack unwinding. This process can be CPU and I/O intensive, particularly on architectures that support DWARF unwinding (arm64 and x86). After the unwind is complete, the information is written to disk synchronously. This prevents data loss if the next line were to crash.

While it is safe to call this API on a background thread, remember that dispatching this call to another queue loses the context of the current stack trace.

What about NSExceptions?

Crashlytics doesn’t offer a facility for logging and recording NSException instances directly. Generally speaking, the Cocoa and Cocoa Touch APIs are not exception-safe. That means the use of @catch can have very serious unintended side-effects in your process, even when used with extreme care. You should never use @catch statements in your code. Please refer to Apple’s documentation on the topic.

Customize stack traces

If your app runs in a non-native environment (such as C++ or Unity), you can use the Exception Model API to report crash metadata in your app's native exception format. Reported exceptions are marked as non-fatals.


var  ex = ExceptionModel(name:"FooException", reason:"There was a foo.")
ex.stackTrace = [
  StackFrame(symbol:"makeError", file:"handler.js", line:495),
  StackFrame(symbol:"then", file:"routes.js", line:102),
  StackFrame(symbol:"main", file:"app.js", line:12),



FIRExceptionModel *model =
    [FIRExceptionModel exceptionModelWithName:@"FooException" reason:@"There was a foo."];
model.stackTrace = @[
  [FIRStackFrame stackFrameWithSymbol:@"makeError" file:@"handler.js" line:495],
  [FIRStackFrame stackFrameWithSymbol:@"then" file:@"routes.js" line:102],
  [FIRStackFrame stackFrameWithSymbol:@"main" file:@"app.js" line:12],

[[FIRCrashlytics crashlytics] recordExceptionModel:model];

Custom stack frames can also be initialized with just addresses:


var  ex = ExceptionModel.init(name:"FooException", reason:"There was a foo.")
ex.stackTrace = [



FIRExceptionModel *model =
    [FIRExceptionModel exceptionModelWithName:@"FooException" reason:@"There was a foo."];
model.stackTrace = @[
  [FIRStackFrame stackFrameWithAddress:0xfa12123],
  [FIRStackFrame stackFrameWithAddress:12412412],
  [FIRStackFrame stackFrameWithAddress:194129124],

[[FIRCrashlytics crashlytics] recordExceptionModel:model];

Get breadcrumb logs

Breadcrumb logs give you a better understanding of the interactions that a user had with your app leading up to a crash, non-fatal, or ANR event. These logs can be helpful when trying to reproduce and debug an issue.

Breadcrumb logs are powered by Google Analytics, so to get breadcrumb logs, you need to enable Google Analytics for your Firebase project and add the Firebase SDK for Google Analytics to your app. Once these requirements are met, breadcrumb logs are automatically included with an event's data within the Logs tab when you view the details of an issue.

The Analytics SDK automatically logs the screen_view event which enables the breadcrumb logs to show a list of screens viewed before the crash, non-fatal, or ANR event. A screen_view breadcrumb log contains a firebase_screen_class parameter.

Breadcrumb logs are also populated with any custom events that you manually log within the user’s session, including the event's parameter data. This data can help show a series of user actions leading up to a crash, non-fatal, or ANR event.

Note that you can control the collection and use of Google Analytics data, which includes the data that populates breadcrumb logs.

Enable opt-in reporting

By default, Crashlytics automatically collects 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 reporting and only sending data to Crashlytics when you choose to in your code:

  1. Turn off automatic collection by adding a new key to your Info.plist file:

    • Key: FirebaseCrashlyticsCollectionEnabled
    • Value: false
  2. Enable collection for select users by calling the Crashlytics data collection override at runtime. The override value persists across launches of your app so Crashlytics can automatically collect reports.

    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.




    [[FIRCrashlytics crashlytics] setCrashlyticsCollectionEnabled:YES];

Manage Crash Insights data

Crash Insights helps you resolve issues by comparing your anonymized stack traces to traces from other Firebase apps and letting you know if your issue is part of a larger trend. For many issues, Crash Insights even provides resources to help you debug the crash.

Crash Insights uses aggregated crash data to identify common stability trends. If you’d prefer not to share your app's data, you can opt-out of Crash Insights from the Crash Insights menu at the top of your Crashlytics issue list in the Firebase console.