> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/getsentry/sentry-javascript/llms.txt
> Use this file to discover all available pages before exploring further.

# SDK Setup

> Learn how to initialize and configure the Sentry JavaScript SDK

The Sentry JavaScript SDK must be initialized as early as possible in your application lifecycle to capture errors and performance data effectively.

## Basic Initialization

The simplest way to initialize Sentry is with just your DSN:

```javascript theme={null}
import * as Sentry from '@sentry/browser';

Sentry.init({
  dsn: 'https://examplePublicKey@o0.ingest.sentry.io/0',
});
```

<Warning>
  Make sure to call `Sentry.init()` as early as possible in your application. Any errors that occur before initialization will not be captured.
</Warning>

## Common Configuration Options

### Release Tracking

Identify your application version to track regressions and know when issues were introduced:

```javascript theme={null}
Sentry.init({
  dsn: '__DSN__',
  release: 'my-app@1.0.0',
});
```

### Environment

Differentiate between production, staging, and development environments:

```javascript theme={null}
Sentry.init({
  dsn: '__DSN__',
  environment: process.env.NODE_ENV || 'development',
});
```

<Tip>
  Set `environment` to help filter issues by deployment environment in Sentry's UI.
</Tip>

### Debug Mode

Enable debug logging during development:

```javascript theme={null}
Sentry.init({
  dsn: '__DSN__',
  debug: true, // Enable debug logging
});
```

## Default Integrations

The SDK includes default integrations that are automatically enabled:

```javascript theme={null}
import * as Sentry from '@sentry/browser';

// These integrations are enabled by default:
// - inboundFiltersIntegration()
// - functionToStringIntegration()
// - conversationIdIntegration()
// - browserApiErrorsIntegration()
// - breadcrumbsIntegration()
// - globalHandlersIntegration()
// - linkedErrorsIntegration()
// - dedupeIntegration()
// - httpContextIntegration()
// - cultureContextIntegration()
// - browserSessionIntegration()

Sentry.init({
  dsn: '__DSN__',
  // Default integrations are included automatically
});
```

### Customizing Integrations

You can add custom integrations or disable default ones:

```javascript theme={null}
Sentry.init({
  dsn: '__DSN__',
  integrations: [
    // Add custom integrations
    Sentry.replayIntegration(),
    Sentry.feedbackIntegration(),
  ],
});
```

To disable default integrations:

```javascript theme={null}
Sentry.init({
  dsn: '__DSN__',
  defaultIntegrations: false, // Disable all defaults
  integrations: [
    // Manually add only the integrations you need
    Sentry.globalHandlersIntegration(),
    Sentry.breadcrumbsIntegration(),
  ],
});
```

## Transport Configuration

By default, the SDK uses `makeFetchTransport`. You can customize the transport:

```javascript theme={null}
import { makeFetchTransport } from '@sentry/browser';

Sentry.init({
  dsn: '__DSN__',
  transport: makeFetchTransport,
  transportOptions: {
    // Custom fetch implementation
    fetchImpl: customFetch,
  },
});
```

### Offline Transport

For applications that need to work offline:

```javascript theme={null}
import { makeBrowserOfflineTransport } from '@sentry/browser';
import { makeFetchTransport } from '@sentry/browser';

Sentry.init({
  dsn: '__DSN__',
  transport: makeBrowserOfflineTransport(makeFetchTransport),
});
```

## Platform-Specific Initialization

### Browser (Vanilla JavaScript)

```javascript theme={null}
import * as Sentry from '@sentry/browser';

Sentry.init({
  dsn: '__DSN__',
  integrations: [Sentry.browserTracingIntegration()],
  tracesSampleRate: 1.0,
});
```

### React

```javascript theme={null}
import * as Sentry from '@sentry/react';

Sentry.init({
  dsn: '__DSN__',
  integrations: [
    Sentry.browserTracingIntegration(),
    Sentry.replayIntegration(),
  ],
  tracesSampleRate: 1.0,
  replaysSessionSampleRate: 0.1,
  replaysOnErrorSampleRate: 1.0,
});
```

### Node.js

<Warning>
  For Node.js, you must initialize Sentry before importing any other modules. In v8+, this is critical for OpenTelemetry instrumentation to work correctly.
</Warning>

```javascript theme={null}
// MUST be the first import!
import * as Sentry from '@sentry/node';

Sentry.init({
  dsn: '__DSN__',
  tracesSampleRate: 1.0,
});

// Now import other modules
import express from 'express';
```

### Next.js

Next.js requires special initialization files. Create these files in your project root:

**instrumentation.ts** (required for Next.js 15+, optional but recommended for 13.2+):

```javascript theme={null}
export async function register() {
  if (process.env.NEXT_RUNTIME === 'nodejs') {
    await import('./sentry.server.config');
  }

  if (process.env.NEXT_RUNTIME === 'edge') {
    await import('./sentry.edge.config');
  }
}
```

**sentry.server.config.ts**:

```javascript theme={null}
import * as Sentry from '@sentry/nextjs';

Sentry.init({
  dsn: '__DSN__',
  tracesSampleRate: 1.0,
});
```

**sentry.client.config.ts**:

```javascript theme={null}
import * as Sentry from '@sentry/nextjs';

Sentry.init({
  dsn: '__DSN__',
  integrations: [
    Sentry.replayIntegration(),
  ],
  tracesSampleRate: 1.0,
  replaysSessionSampleRate: 0.1,
  replaysOnErrorSampleRate: 1.0,
});
```

## Verifying Your Setup

After initialization, test that events are being sent:

```javascript theme={null}
Sentry.init({
  dsn: '__DSN__',
});

// Send a test error
Sentry.captureException(new Error('Test error'));

// Send a test message
Sentry.captureMessage('Test message');
```

You should see these events appear in your Sentry project within a few seconds.

## Next Steps

<CardGroup cols={2}>
  <Card title="Environment Configuration" href="/guides/configuration/environment">
    Configure environment-specific settings
  </Card>

  <Card title="Sampling" href="/guides/configuration/sampling">
    Control data volume with sampling
  </Card>

  <Card title="Filtering" href="/guides/configuration/filtering">
    Filter events before sending to Sentry
  </Card>

  <Card title="Performance Monitoring" href="/guides/best-practices/performance">
    Set up performance monitoring
  </Card>
</CardGroup>