Performance Monitoring uses traces to collect data about monitored processes in your app. A trace is a report that contains data captured between two points in time in your app.
For iOS and Android apps, Performance Monitoring automatically collects several traces related to app lifecycle. All these traces are like timers because they measure the time it takes for the process to run (the "duration").
App start trace — A trace that measures the time between when the user opens the app and when the app is responsive
App-in-foreground trace — A trace that measures the time when the app is running in the foreground and available to the user
App-in-background trace — A trace that measures the time when the app is running in the background
View data from these traces in the On device tab of the Firebase console (learn more later on this page). Note that since these traces only collect the metric "duration", they are sometimes called "Duration traces". Also, in the Firebase console (in the On device tab), these traces are grouped under the table labeled Durations.
Definitions for each trace
Performance Monitoring uses method calls and notifications in your app to determine when each type of trace starts and stops. All these traces are like timers because they measure the time it takes for the process to run.
App start trace
This trace measures the time between when the user opens the app and when the
app is responsive. In the console, the trace's name is _app_start
. The
collected metric for this trace is "duration".
Starts when the application loads the first
Object
to memory.Stops after the first successful run loop that occurs after the application receives the
UIApplicationDidBecomeActiveNotification
notification.
App-in-foreground trace
This trace measures the time when the app is running in the foreground and
available to the user. In the console, the trace's name is _app_in_foreground
.
The collected metric for this trace is "duration".
Starts when the application receives the
UIApplicationDidBecomeActiveNotification
notification.Stops when it receives the
UIApplicationWillResignActiveNotification
notification.
App-in-background trace
This trace measures the time when the app is running in the background. In the
console, the trace's name is _app_in_background
. The reported metric for this
trace is "duration".
Starts when the application receives the
UIApplicationWillResignActiveNotification
notification.Stops when it receives the
UIApplicationDidBecomeActiveNotification
notification.
Metrics collected by these traces
These traces are out-of-the-box traces, so you cannot add custom metrics or custom attributes to them.
All these traces are like timers because they measure the time it takes for the monitored process to run. The name of this collected metric is called "duration".
Track, view, and filter performance data
Track key metrics in your dashboard
Add your key metrics to your dashboard to learn how they're trending. You can quickly identify regressions by seeing week-over-week changes or verify that recent changes in your code are improving performance.

To add a metric to your dashboard, go to the Performance dashboard in the Firebase console, then click the Dashboard tab. Click an empty metric card, then select an existing metric to add to your dashboard. Click on a populated metric card for more options, like to replace or remove a metric.
The dashboard shows collected metric data over time, both in graphical form and as a numerical percentage change.
Learn more about using the dashboard.
View all traces and their data
To view these traces, go to the Performance dashboard in the Firebase console, then click the On device tab.
From the On Device tab, you can click through various screens to explore a trace and
drill down into metrics of interest. On most pages, you can use the

- Filter by App version to view data about a past release or your latest release
- Filter by Device to learn how older devices handle your app
- Filter by Country to make sure your database location isn't affecting a specific region
Learn more about viewing data for your traces.
Next Steps
Learn more about using attributes to examine performance data.
Learn more about how to track performance issues in the Firebase console.
- View detailed reports of user sessions in which you can see a specific trace in a timeline context of other traces collected during the same session.