---
title: "Tracing"
description: "Learn how to enable tracing in your app and get valuable performance insights about your application."
url: https://docs.sentry.io/platforms/apple/guides/ios/tracing/
---

# Set Up Tracing | Sentry for iOS

With [tracing](https://docs.sentry.io/product/dashboards/sentry-dashboards.md), Sentry tracks your software performance, measuring metrics like throughput and latency, and displaying the impact of errors across multiple systems. Sentry captures distributed traces consisting of transactions and spans, which measure individual services and individual operations within those services. Learn more about our model in [Distributed Tracing](https://docs.sentry.io/product/sentry-basics/tracing/distributed-tracing.md).

Automatic instrumentation for monitoring the performance of your application is currently in preview. You can also use custom instrumentation to capture transactions.

## [Configure](https://docs.sentry.io/platforms/apple/guides/ios/tracing.md#configure)

First, enable tracing and configure the sample rate for transactions. Set the sample rate for your transactions by either:

* Setting a uniform sample rate for all transactions using the `tracesSampleRate` option in your SDK config to a number between `0` and `1`. (For example, to send 20% of transactions, set `tracesSampleRate` to `0.2`.)
* Controlling the sample rate based on the transaction itself and the context in which it's captured, by providing a function to the `tracesSampler` config option.

The two options are meant to be mutually exclusive. If you set both, `tracesSampler` will take precedence.

```swift
import Sentry

SentrySDK.start { options in
    options.dsn = "https://<key>@o<orgId>.ingest.sentry.io/<projectId>"

+   // Example uniform sample rate: capture 100% of transactions
+   // In Production you will probably want a smaller number such as 0.5 for 50%
+   options.tracesSampleRate = 1.0

+   // OR if you prefer, determine traces sample rate based on the
+   // sampling context
+   options.tracesSampler = { context in
+       // Don't miss any transactions for VIP users
+       if context.customSamplingContext?["vip"] as? Bool == true {
+           return 1.0
+       } else {
+           return 0.25 // 25% for everything else
+       }
+   }
}
```

*Other available variations of the above snippet: objc, objc*

Learn more about tracing [options](https://docs.sentry.io/platforms/apple/guides/ios/configuration/options.md#tracing-options), how to use the [tracesSampler](https://docs.sentry.io/platforms/apple/guides/ios/configuration/sampling.md#setting-a-sampling-function) function, or how to [sample transactions](https://docs.sentry.io/platforms/apple/guides/ios/configuration/sampling.md#sampling-transaction-events).

## [Verify](https://docs.sentry.io/platforms/apple/guides/ios/tracing.md#verify)

Verify that tracing is working correctly by using our [automatic instrumentation](https://docs.sentry.io/platforms/apple/guides/ios/tracing/instrumentation/automatic-instrumentation.md) or by starting and finishing a transaction using [custom instrumentation](https://docs.sentry.io/platforms/apple/guides/ios/tracing/instrumentation/custom-instrumentation.md).

Test out tracing by starting and finishing a transaction, which you *must* do so transactions can be sent to Sentry. Learn how in our [Custom Instrumentation](https://docs.sentry.io/platforms/apple/guides/ios/tracing/instrumentation/custom-instrumentation.md) content.

While you're testing, set `tracesSampleRate` to `1.0`, as that ensures that every transaction will be sent to Sentry. Once testing is complete, you may want to set a lower `tracesSampleRate` value, or switch to using `tracesSampler` to selectively sample and filter your transactions, based on contextual data.

## [Standalone App Start Tracing](https://docs.sentry.io/platforms/apple/guides/ios/tracing.md#standalone-app-start-tracing)

This feature is experimental. The API is subject to change and may introduce breaking changes in future releases.

By default, app start data is attached as spans to the first transaction in your app. Standalone app start tracing sends app start data as its own separate transaction instead. This gives you more accurate app start measurements, since they aren't dependent on another transaction being started.

To enable standalone app start tracing, add the following to your SDK configuration:

```swift
import Sentry

SentrySDK.start { options in
    options.experimental.enableStandaloneAppStartTracing = true
}
```

*Other available variations of the above snippet: objc*

The SDK must be initialized before the `didFinishLaunchingNotification` is posted for standalone app start tracing to work. In practice, this means calling `SentrySDK.start` inside your `application(_:didFinishLaunchingWithOptions:)` method (UIKit) or your `App` conformer's `init()` (SwiftUI). If the SDK is started later, the standalone app start transaction may never finish.

For more details on app start instrumentation, see [App Start Tracing](https://docs.sentry.io/platforms/apple/guides/ios/tracing/instrumentation/automatic-instrumentation.md#app-start-tracing).

## [Next Steps](https://docs.sentry.io/platforms/apple/guides/ios/tracing.md#next-steps)

* #### [Instrumentation](https://docs.sentry.io/platforms/apple/guides/ios/tracing/instrumentation.md)

  Learn how to instrument tracing in your app.

* #### [Trace Propagation](https://docs.sentry.io/platforms/apple/guides/ios/tracing/trace-propagation.md)

  Learn how to connect events across applications/services.

## Pages in this section

- [Instrumentation](https://docs.sentry.io/platforms/apple/guides/ios/tracing/instrumentation.md)
- [Trace Propagation](https://docs.sentry.io/platforms/apple/guides/ios/tracing/trace-propagation.md)