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Debug your Android app based on ANR tags in the Crashlytics dashboard

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Application Not Responding (ANR) errors are triggered when the UI thread of the application is not responding for more than 5 seconds. You can read more about ANRs and diagnosing ANRs in the Android documentation.

Additionally, Crashlytics can help pinpoint specific problematic threads. We analyze ANRs, and then, in the Crashlytics dashboard, we tag applicable threads to provide hints on how to debug the ANR.

The following sections on this page explain what each ANR tag means, shows an example ANR with that tag, and provides a recommended solution to debug the ANR.

Triggered ANR

A thread which was blocked for too long and triggered the ANR is annotated with this Triggered ANR tag.

The problematic thread can be the main thread for the app, or any thread found to be unresponsive. However, the thread tagged as Triggered ANR may or may not be the actual cause of the ANR. To provide insights for debugging and fixing these ANRs, Crashlytics also tags any other threads that are involved in the ANR. In the following sections of this page, learn about the other tags that could be applied to a thread.


Any threads which are found to be involved in a deadlock that led to the ANR are annotated with this Deadlocked tag.

A deadlock occurs when a thread enters a waiting state because a required resource is held by another thread, which is also waiting for a resource held by the first thread. If the app's main thread is in this situation, ANRs are likely to happen.


Look at threads involved in the deadlock and check the resources/locks acquired by those threads. Refer to Deadlock and Deadlock prevention algorithms for possible solutions.

IO Root blocking

Any thread that was executing slow I/O operations and blocked the Triggered ANR thread is annotated with the IO Root blocking tag. If the Triggered ANR thread isn’t blocked by other threads, then the IO Root blocking thread is also a Root blocking thread.


In general, your app shouldn't execute expensive I/O operations on the main thread. In the case of the main thread being IO Root blocking, you can also use Strict Mode to identify any unintentional I/O operations that are happening on the main thread.

Root blocking

Any thread that blocked the thread tagged as Triggered ANR is annotated with the Root blocking tag. If a thread is tagged as both Root blocking and Triggered ANR, then there are no other threads that block that thread.

If any Triggered ANR threads were waiting (maybe transitively) for other threads, they are Root blocking. There could be various reasons why a thread is a root cause of the ANR.


Minimize CPU intensive work in the main thread. Use worker or background threads for performing CPU intensive tasks.

Minimize I/O intensive work, like loading from a database, on the main thread.

Unknown root cause

A thread is tagged with the Unknown root cause tag if it was the thread that triggered the ANR but was idle in the process when the ANR occurred. Crashlytics doesn't have sufficient information to determine the root cause. There is no evident reason why this ANR has occurred.


Follow the general advice on how to prevent ANRs. For example, identify the places in your code where the app’s main thread can be busy for more than 5 seconds.