sentry-error-capture

# Sentry Error Capture

## Overview

Capture errors and enrich them with structured context so your team can diagnose production issues in seconds instead of hours. Covers `captureException`, `captureMessage`, scoped context (`withScope` / `push_scope`), breadcrumbs, custom fingerprinting, and `beforeSend` filtering using `@sentry/node` v8 and `sentry-sdk` v2 APIs.

## Prerequisites

- Sentry SDK installed and initialized (`@sentry/node` v8+ or `sentry-sdk` v2+)
- A valid DSN configured via environment variable (`SENTRY_DSN`)
- Understanding of try/catch (JS) or try/except (Python) error handling
- A Sentry project created at [sentry.io](https://sentry.io)

## Instructions

### Step 1 -- Capture Exceptions with Full Stack Traces

Always pass real `Error` objects (or Python exception instances), never plain strings. Plain strings lose the stack trace, making debugging far harder.

**TypeScript (`@sentry/node`)**

```typescript
import * as Sentry from '@sentry/node';

// CORRECT -- full stack trace preserved
try {
  await riskyOperation();
} catch (error) {
  Sentry.captureException(error);
}

// WRONG -- no stack trace, hard to debug
Sentry.captureException('something went wrong');

// Wrapping non-Error values into proper Error objects
Sentry.captureException(new Error(`API returned ${statusCode}: ${body}`));

// Capture with inline context (no scope needed for simple cases)
Sentry.captureException(error, {
  tags: { transaction: 'purchase' },
  extra: { orderId, amount },
});
```

**Python (`sentry-sdk`)**

```python
import sentry_sdk

# CORRECT -- full traceback preserved
try:
    risky_operation()
except Exception as e:
    sentry_sdk.capture_exception(e)

# Capture current exception implicitly (inside except block)
try:
    risky_operation()
except Exception:
    sentry_sdk.capture_exception()  # captures sys.exc_info() automatically
```

### Step 2 -- Capture Messages for Non-Exception Events

Use `captureMessage` for events that are not exceptions but still worth tracking: deprecation warnings, capacity thresholds, business logic anomalies.

**TypeScript**

```typescript
// Severity levels: 'fatal' | 'error' | 'warning' | 'info' | 'debug' | 'log'
Sentry.captureMessage('Payment processed successfully', 'info');
Sentry.captureMessage('Deprecated API endpoint accessed', 'warning');
Sentry.captureMessage('Database connection pool exhausted', 'fatal');
```

**Python**

```python
sentry_sdk.capture_message("Payment gateway timeout", level="warning")
sentry_sdk.capture_message("Daily report generated", level="info")
sentry_sdk.capture_message("Connection pool exhausted", level="fatal")
```

### Step 3 -- Enrich Events with Scoped Context

Use `withScope` (TypeScript) or `push_scope` (Python) to attach context to a single event without polluting the global scope. Context is automatically cleaned up when the scope exits.

**TypeScript -- withScope**

```typescript
Sentry.withScope((scope) => {
  // User identity for issue assignment and impact analysis
  scope.setUser({
    id: user.id,
    email: user.email,
    subscription: user.plan,
  });

  // Tags: indexed, searchable in Sentry UI filters
  scope.setTag('payment_provider', 'stripe');
  scope.setTag('feature', 'checkout');

  // Structured context: visible in event detail sidebar
  scope.setContext('payment', {
    amount: 9999,
    currency: 'USD',
    customer_id: 'cus_abc123',
    idempotency_key: 'idem_xyz789',
  });

  // Extra data: arbitrary key-value pairs for debugging
  scope.setExtra('cart', cartItems);

  // Override severity level
  scope.setLevel('fatal');

  // Custom fingerprint to control issue grouping
  scope.setFingerprint(['checkout-failure', paymentProvider]);

  Sentry.captureException(error);
});
// Scope is automatically cleaned up -- global scope unchanged
```

**Python -- push_scope**

```python
with sentry_sdk.push_scope() as scope:
    scope.user = {"id": user_id, "email": user_email}
    scope.set_tag("feature", "checkout")
    scope.set_extra("cart", cart_items)
    scope.level = "fatal"
    scope.fingerprint = ["checkout-failure", str(error_code)]
    sentry_sdk.capture_exception(error)
# Scope is automatically cleaned up
```

## Breadcrumbs

Breadcrumbs create a trail of events leading up to an error. Sentry auto-captures some (console logs, HTTP requests, DOM events), but manual breadcrumbs add domain-specific context.

**TypeScript**

```typescript
Sentry.addBreadcrumb({
  category: 'auth',
  message: `User ${userId} logged in via ${provider}`,
  level: 'info',
  data: { provider, method: 'oauth2' },
});

Sentry.addBreadcrumb({
  category: 'transaction',
  message: 'Payment initiated',
  level: 'info',
  data: { amount: 49.99, items: 3 },
});
// The next captured error includes all breadcrumbs above
```

**Python**

```python
sentry_sdk.add_breadcrumb(
    category="auth",
    message=f"User {user_id} logged in via {provider}",
    level="info",
    data={"provider": provider, "method": "oauth2"},
)

sentry_sdk.add_breadcrumb(
    category="transaction",
    message="Payment initiated",
    level="info",
    data={"amount": 49.99, "items": 3},
)
```

## Custom Fingerprinting

Override Sentry's default grouping to control how errors are merged into issues. Without custom fingerprints, Sentry groups by stack trace, which can split logically identical errors or merge unrelated ones.

```typescript
// Group all timeout errors for /api/search into one issue
Sentry.withScope((scope) => {
  scope.setFingerprint(['api-timeout', 'search-endpoint']);
  Sentry.captureException(new Error('Search API timeout'));
});

// Group by error type + HTTP status + endpoint
Sentry.withScope((scope) => {
  scope.setFingerprint(['http-error', String(response.status), endpoint]);
  Sentry.captureException(error);
});

// Use {{ default }} to extend rather than replace default grouping
Sentry.withScope((scope) => {
  scope.setFingerprint(['{{ default }}', tenantId]);
  Sentry.captureException(error);
});
```

## Global Filtering with beforeSend

Configure `beforeSend` during initialization to filter noise, scrub sensitive data, or enrich all events globally.

```typescript
Sentry.init({
  dsn: process.env.SENTRY_DSN,
  beforeSend(event, hint) {
    const error = hint?.originalException;

    // Drop specific error types
    if (error instanceof AbortError) return null;
    if (error?.message?.match(/ResizeObserver loop/)) return null;

    // Scrub sensitive headers
    if (event.request?.headers) {
      delete event.request.headers['Authorization'];
      delete event.request.headers['Cookie'];
    }

    // Enrich database errors with subsystem tag
    if (error instanceof DatabaseError) {
      event.tags = { ...event.tags, subsystem: 'database' };
      event.level = 'fatal';
    }

    return event; // Must return event or null
  },

  // Pattern-based noise filtering
  ignoreErrors: [
    'ResizeObserver loop',
    'Non-Error promise rejection',
    /Loading chunk \d+ failed/,
    'Network request failed',
  ],
});
```

## Output

- Errors with full stack traces and context in the Sentry Issues dashboard
- Scoped tags and structured context for filtering and search
- Breadcrumb trails showing the user journey before errors
- Custom fingerprints grouping related errors into single issues
- Clean event stream via `beforeSend` filtering and `ignoreErrors`

## Error Handling

| Error | Cause | Solution |
|-------|-------|----------|
| Missing stack trace | String passed instead of Error object | Always use `new Error()` or extend the Error class |
| Events not grouped properly | Default fingerprinting insufficient | Use `scope.setFingerprint()` with domain-specific keys |
| `beforeSend` dropping all events | Function returns `undefined` | Always return `event` or explicitly `null` |
| Scope leaking between requests | Global scope modified in async context | Use `withScope()` / `push_scope()` for per-request context |
| Too many events hitting quota | No filtering or sampling configured | Add `ignoreErrors`, `beforeSend` filters, or `sampleRate` |
| Context not showing in Sentry UI | Used `setExtra` for structured data | Use `setContext('name', {...})` for sidebar visibility |

## Examples

### TypeScript -- Express Route with Context

```typescript
import express from 'express';
import * as Sentry from '@sentry/node';

const app = express();
Sentry.setupExpressErrorHandler(app);

app.get('/api/users/:id', async (req, res) => {
  Sentry.setUser({ id: req.params.id });
  try {
    const user = await getUser(req.params.id);
    res.json(user);
  } catch (error) {
    Sentry.withScope((scope) => {
      scope.setContext('request', {
        params: req.params,
        query: req.query,
        method: req.method,
      });
      Sentry.captureException(error);
    });
    res.status(500).json({ error: 'Internal server error' });
  }
});
```

### TypeScript -- Batch Processing with Promise.allSettled

```typescript
async function processQueue(items: QueueItem[]) {
  const results = await Promise.allSettled(
    items.map(item => processItem(item))
  );
  results.forEach((result, index) => {
    if (result.status === 'rejected') {
      Sentry.withScope((scope) => {
        scope.setTag('queue_item_index', String(index));
        scope.setContext('item', items[index]);
        Sentry.captureException(result.reason);
      });
    }
  });
}
```

### Python -- Background Job Error

```python
import sentry_sdk

def process_report(report_id: str, user_id: str):
    sentry_sdk.add_breadcrumb(
        category="jobs",
        message=f"Report generation started: {report_id}",
        level="info",
    )
    try:
        data = fetch_report_data(report_id)
        return generate_pdf(data)
    except Exception as error:
        with sentry_sdk.push_scope() as scope:
            scope.user = {"id": user_id}
            scope.set_tag("job_type", "report_generation")
            scope.set_context("report", {
                "report_id": report_id,
                "stage": "pdf_generation",
            })
            scope.fingerprint = ["report-failure", report_id]
            sentry_sdk.capture_exception(error)
        raise
```

## Resources

- [Capturing Errors](https://docs.sentry.io/platforms/javascript/usage/) -- `captureException` and `captureMessage` reference
- [Scopes and Context](https://docs.sentry.io/platforms/javascript/enriching-events/scopes/) -- `withScope`, `setUser`, `setTag`, `setContext`
- [Breadcrumbs](https://docs.sentry.io/platforms/javascript/enriching-events/breadcrumbs/) -- manual and auto-captured breadcrumbs
- [Filtering Events](https://docs.sentry.io/platforms/javascript/configuration/filtering/) -- `beforeSend`, `ignoreErrors`, sampling
- [Issue Grouping](https://docs.sentry.io/product/data-management-settings/event-grouping/) -- fingerprinting and merge/unmerge
- [Python SDK Usage](https://docs.sentry.io/platforms/python/usage/) -- Python-specific capture patterns

## Next Steps

- **Performance tracing**: Add `Sentry.startSpan()` to measure operation timing (see `sentry-performance-tracing`)
- **Release management**: Tag errors with release versions for regression detection (see `sentry-release-management`)
- **Cost tuning**: Configure `sampleRate` and `tracesSampleRate` to control event volume (see `sentry-cost-tuning`)