---
title: "Tracing"
description: "Learn how to enable tracing in your app."
url: https://docs.sentry.io/platforms/javascript/tracing/
---

# Set Up Tracing | Sentry for JavaScript

With [tracing](https://docs.sentry.io/product/insights/overview.md), Sentry automatically tracks your software performance across your application services, measuring metrics like throughput and latency, and displaying the impact of errors across multiple systems.

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

Enable tracing by configuring the sampling rate for traces. Set the sample rate as follows:

```javascript
import * as Sentry from "___SDK_PACKAGE___";

Sentry.init({
  dsn: "___PUBLIC_DSN___",

  // This enables automatic instrumentation (highly recommended),
  // but is not necessary for purely manual usage
  // If you only want to use custom instrumentation:
  // * Remove the `BrowserTracing` integration
  // * add `Sentry.addTracingExtensions()` above your Sentry.init() call
  integrations: [Sentry.browserTracingIntegration()],

  // We recommend adjusting this value in production, or using tracesSampler
  // for finer control
  tracesSampleRate: 1.0,

  // Set `tracePropagationTargets` to control for which URLs trace propagation should be enabled
  tracePropagationTargets: ["localhost", /^https:\/\/yourserver\.io\/api/],
});
```

* You can establish a uniform sample rate for all transactions by setting 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`.)
* For more granular control over sampling, you can set 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 mutually exclusive. If both are set, `tracesSampler` will take precedence.

You can find more in-depth explanations and examples about sampling configuration in [Configure Sampling](https://docs.sentry.io/platforms/javascript/tracing/configure-sampling.md).

## [Distributed Tracing](https://docs.sentry.io/platforms/javascript/tracing.md#distributed-tracing)

Sentry captures distributed traces consisting of transactions and spans, which measure individual services and individual operations within those services, respectively. Learn more about our model in [Distributed Tracing](https://docs.sentry.io/product/sentry-basics/tracing/distributed-tracing.md).

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

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

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.

If you leave your sample rate at `1.0`, a transaction will be sent every time a user loads a page or navigates within your app. Depending on the amount of traffic your application gets, this may mean a lot of transactions. If you have a high-load, backend application, you may want to consider setting a lower `tracesSampleRate` value, or switching to using `tracesSampler` to selectively sample and filter your transactions, based on contextual data.

## [Automatic Instrumentation](https://docs.sentry.io/platforms/javascript/tracing.md#automatic-instrumentation)

See [Automatic Instrumentation](https://docs.sentry.io/platforms/javascript/tracing/instrumentation/automatic-instrumentation.md) to learn about all the things that the SDK automatically instruments for you.

## [Custom Instrumentation](https://docs.sentry.io/platforms/javascript/tracing.md#custom-instrumentation)

You can also manually start spans to instrument specific parts of your code. This is useful when you want to measure the performance of a specific operation or function.

* [Tracing APIs](https://docs.sentry.io/platforms/javascript/apis.md#tracing): Find information about APIs for custom tracing instrumentation
* [Instrumentation](https://docs.sentry.io/platforms/javascript/tracing/instrumentation.md): Find information about manual instrumentation with the Sentry SDK
* [Sending Span Metrics](https://docs.sentry.io/platforms/javascript/tracing/span-metrics.md): Learn how to capture metrics on your spans

## [Replay Linking](https://docs.sentry.io/platforms/javascript/tracing.md#replay-linking)

When [Session Replay](https://docs.sentry.io/product/explore/session-replay.md) is enabled, traces appear in the Replay timeline. This lets you correlate performance data with exactly what the user was seeing and doing.

From any trace, click the replay link to jump directly to the replay and see the user's experience during that operation. From a replay, click any trace span in the timeline to drill into performance details.

This bidirectional linking helps you understand not just *how long* something took, but *what impact* it had on the user's experience.

## [Disabling Tracing](https://docs.sentry.io/platforms/javascript/tracing.md#disabling-tracing)

If you want to disable tracing, you *should not* set `tracesSampleRate` at all. Setting it to `0` will not disable tracing, it will simply never send any traces to Sentry. Instead, neither `tracesSampleRate` nor `tracesSampler` should be defined in your SDK config to fully disable tracing.

## [Related Features](https://docs.sentry.io/platforms/javascript/tracing.md#related-features)

* [Session Replay](https://docs.sentry.io/platforms/javascript/session-replay.md) — Traces appear in the Replay timeline, showing performance data alongside the user's actions.
* [Logs](https://docs.sentry.io/platforms/javascript/logs.md) — Logs emitted during a trace are automatically linked, giving you diagnostic context for each operation.

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

* #### [Sending Span Metrics](https://docs.sentry.io/platforms/javascript/tracing/span-metrics.md)

  Learn how to add attributes to spans to monitor performance and debug applications

* #### [Set Up Distributed Tracing](https://docs.sentry.io/platforms/javascript/tracing/distributed-tracing.md)

  Learn how to connect events across applications/services.

* #### [Configure Sampling](https://docs.sentry.io/platforms/javascript/tracing/configure-sampling.md)

  Learn how to configure sampling in your app.

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

  Learn how to configure spans to capture trace data on any action in your app.

* #### [Troubleshooting](https://docs.sentry.io/platforms/javascript/tracing/troubleshooting.md)

  Learn how to troubleshoot your tracing setup.

## Pages in this section

- [Sending Span Metrics](https://docs.sentry.io/platforms/javascript/tracing/span-metrics.md)
- [Set Up Distributed Tracing](https://docs.sentry.io/platforms/javascript/tracing/distributed-tracing.md)
- [Configure Sampling](https://docs.sentry.io/platforms/javascript/tracing/configure-sampling.md)
- [Instrumentation](https://docs.sentry.io/platforms/javascript/tracing/instrumentation.md)
- [Troubleshooting](https://docs.sentry.io/platforms/javascript/tracing/troubleshooting.md)