Setup Sentry Tracing

This skill helps configure Sentry's Tracing (Performance Monitoring) to track application performance, measure latency, and create distributed traces across services.

When to Use This Skill

Invoke this skill when:

• User asks to "setup tracing" or "enable performance monitoring"
• User wants to "track transactions" or "measure latency"
• User requests "distributed tracing" or "span instrumentation"
• User mentions tracking API response times or page load performance
• User asks about tracesSampleRate or custom spans

Platform Detection

Before configuring, detect the project's platform:

JavaScript/TypeScript

Check package.json for:

• @sentry/nextjs - Next.js
• @sentry/react - React
• @sentry/node - Node.js
• @sentry/browser - Browser/vanilla JS
• @sentry/vue - Vue
• @sentry/angular - Angular
• @sentry/sveltekit - SvelteKit

Python

Check for sentry-sdk in requirements

Ruby

Check for sentry-ruby in Gemfile

---

Core Concepts

Explain these concepts to the user:

Concept	Description
Trace	Complete journey of a request across services
Transaction	Single instance of a service being called (root span)
Span	Individual unit of work within a transaction
Sample Rate	Percentage of transactions to capture (0-1)

---

JavaScript/TypeScript Configuration

Step 1: Locate Sentry Init

Find the Sentry.init() call:

• Next.js: instrumentation-client.ts, sentry.server.config.ts, sentry.edge.config.ts
• React: src/index.tsx or entry file
• Node.js: Entry point or config file
• Vue/Angular: Main app initialization

Step 2: Enable Tracing

Browser/React - Add browserTracingIntegration

import * as Sentry from "@sentry/react"; // or @sentry/browser

Sentry.init({
  dsn: "YOUR_DSN_HERE",

  // Add browser tracing integration
  integrations: [Sentry.browserTracingIntegration()],

  // Set sample rate (1.0 = 100% for testing, lower for production)
  tracesSampleRate: 1.0,

  // Configure which URLs receive trace headers for distributed tracing
  tracePropagationTargets: [
    "localhost",
    /^https:\/\/yourserver\.io\/api/,
  ],
});

Next.js - Configure All Init Files

Client (instrumentation-client.ts):

import * as Sentry from "@sentry/nextjs";

Sentry.init({
  dsn: "YOUR_DSN_HERE",
  tracesSampleRate: 1.0,
  // Browser tracing is automatic in @sentry/nextjs
});

Server (sentry.server.config.ts):

import * as Sentry from "@sentry/nextjs";

Sentry.init({
  dsn: "YOUR_DSN_HERE",
  tracesSampleRate: 1.0,
});

Edge (sentry.edge.config.ts):

import * as Sentry from "@sentry/nextjs";

Sentry.init({
  dsn: "YOUR_DSN_HERE",
  tracesSampleRate: 1.0,
});

Next.js 14+ App Router Requirement:

For distributed tracing in App Router, add trace data to root layout metadata:

// app/layout.tsx
import * as Sentry from "@sentry/nextjs";

export async function generateMetadata() {
  return {
    other: {
      ...Sentry.getTraceData(),
    },
  };
}

Node.js

const Sentry = require("@sentry/node");

Sentry.init({
  dsn: "YOUR_DSN_HERE",
  tracesSampleRate: 1.0,
});

Step 3: Configure Sampling

Option A: Uniform Sample Rate (Simple)

Sentry.init({
  // Capture 20% of all transactions
  tracesSampleRate: 0.2,
});

Option B: Dynamic Sampling (Advanced)

Sentry.init({
  tracesSampler: ({ name, attributes, parentSampled }) => {
    // Always skip health checks
    if (name.includes("healthcheck")) {
      return 0;
    }

    // Always capture auth transactions
    if (name.includes("auth")) {
      return 1;
    }

    // Sample comments at 1%
    if (name.includes("comment")) {
      return 0.01;
    }

    // Inherit parent sampling decision if available
    if (typeof parentSampled === "boolean") {
      return parentSampled;
    }

    // Default: 50%
    return 0.5;
  },
});

Note: If both tracesSampleRate and tracesSampler are set, tracesSampler takes precedence.

---

Browser Tracing Integration Options

The browserTracingIntegration() accepts many configuration options:

Sentry.init({
  integrations: [
    Sentry.browserTracingIntegration({
      // Trace propagation targets (which URLs get trace headers)
      tracePropagationTargets: ["localhost", /^https:\/\/api\./],

      // Modify spans before creation (e.g., parameterize URLs)
      beforeStartSpan: (context) => {
        return {
          ...context,
          name: context.name.replace(/\/users\/\d+/, "/users/:id"),
        };
      },

      // Filter unwanted spans
      shouldCreateSpanForRequest: (url) => {
        return !url.includes("healthcheck");
      },

      // Timing configurations
      idleTimeout: 1000,        // ms before finishing idle spans
      finalTimeout: 30000,      // max span duration
      childSpanTimeout: 15000,  // max child span duration

      // Feature toggles
      instrumentNavigation: true,  // Track URL changes
      instrumentPageLoad: true,    // Track initial page load
      enableLongTask: true,        // Track long tasks
      enableInp: true,             // Track Interaction to Next Paint

      // INP sampling (separate from tracesSampleRate)
      interactionsSampleRate: 1.0,
    }),
  ],
});

---

Python Configuration

Step 1: Enable Tracing

import sentry_sdk

sentry_sdk.init(
    dsn="YOUR_DSN_HERE",
    traces_sample_rate=1.0,  # 100% for testing
)

Step 2: Configure Sampling

Uniform Rate

sentry_sdk.init(
    dsn="YOUR_DSN_HERE",
    traces_sample_rate=0.2,  # 20% of transactions
)

Dynamic Sampling

def traces_sampler(sampling_context):
    transaction_name = sampling_context.get("transaction_context", {}).get("name", "")

    if "healthcheck" in transaction_name:
        return 0

    if "auth" in transaction_name:
        return 1.0

    # Inherit from parent if available
    if sampling_context.get("parent_sampled") is not None:
        return sampling_context["parent_sampled"]

    return 0.5

sentry_sdk.init(
    dsn="YOUR_DSN_HERE",
    traces_sampler=traces_sampler,
)

---

Ruby Configuration

Enable Tracing

Sentry.init do |config|
  config.dsn = "YOUR_DSN_HERE"
  config.traces_sample_rate = 1.0  # 100% for testing
end

Dynamic Sampling

Sentry.init do |config|
  config.dsn = "YOUR_DSN_HERE"

  config.traces_sampler = lambda do |sampling_context|
    transaction_name = sampling_context[:transaction_context][:name]

    return 0 if transaction_name.include?("healthcheck")
    return 1.0 if transaction_name.include?("auth")

    0.5  # Default 50%
  end
end

---

Custom Instrumentation

JavaScript Custom Spans

Using startSpan (Recommended)

// Synchronous operation
const result = Sentry.startSpan(
  { name: "expensive-calculation", op: "function" },
  () => {
    return calculateSomething();
  }
);

// Async operation
const result = await Sentry.startSpan(
  { name: "fetch-user-data", op: "http.client" },
  async () => {
    const response = await fetch("/api/user");
    return response.json();
  }
);

// With attributes
const result = await Sentry.startSpan(
  {
    name: "process-order",
    op: "task",
    attributes: {
      "order.id": orderId,
      "order.amount": amount,
    },
  },
  async () => {
    return processOrder(orderId);
  }
);

Nested Spans

await Sentry.startSpan({ name: "checkout-flow", op: "transaction" }, async () => {
  // Child span 1
  await Sentry.startSpan({ name: "validate-cart", op: "validation" }, async () => {
    await validateCart();
  });

  // Child span 2
  await Sentry.startSpan({ name: "process-payment", op: "payment" }, async () => {
    await processPayment();
  });

  // Child span 3
  await Sentry.startSpan({ name: "send-confirmation", op: "email" }, async () => {
    await sendConfirmationEmail();
  });
});

Manual Span Control

function middleware(req, res, next) {
  return Sentry.startSpanManual({ name: "middleware", op: "middleware" }, (span) => {
    res.once("finish", () => {
      span.setStatus({ code: res.statusCode < 400 ? 1 : 2 });
      span.end();
    });
    return next();
  });
}

Inactive Spans (Browser)

let checkoutSpan;

// Start inactive span
function onStartCheckout() {
  checkoutSpan = Sentry.startInactiveSpan({ name: "checkout-flow" });
  Sentry.setActiveSpanInBrowser(checkoutSpan);
}

// End when done
function onCompleteCheckout() {
  checkoutSpan?.end();
}

Python Custom Spans

Using Decorator (Simplest)

import sentry_sdk

@sentry_sdk.trace
def expensive_function():
    # Automatically creates a span
    return do_work()

# With parameters (SDK 2.35.0+)
@sentry_sdk.trace(op="database", name="fetch-users")
def fetch_users():
    return db.query(User).all()

Using Context Manager

import sentry_sdk

def process_order(order_id):
    with sentry_sdk.start_span(name="process-order", op="task") as span:
        span.set_data("order.id", order_id)

        # Nested span
        with sentry_sdk.start_span(name="validate-order", op="validation"):
            validate(order_id)

        with sentry_sdk.start_span(name="charge-payment", op="payment"):
            charge(order_id)

        return {"success": True}

Manual Transaction

import sentry_sdk

with sentry_sdk.start_transaction(op="task", name="batch-process") as transaction:
    for item in items:
        with sentry_sdk.start_span(name=f"process-item-{item.id}"):
            process(item)

    transaction.set_tag("items_processed", len(items))

Centralized Configuration

sentry_sdk.init(
    dsn="YOUR_DSN_HERE",
    traces_sample_rate=1.0,
    functions_to_trace=[
        {"qualified_name": "myapp.services.process_order"},
        {"qualified_name": "myapp.services.send_notification"},
    ],
)

---

Distributed Tracing

How It Works

Sentry propagates trace context via HTTP headers:

• sentry-trace: Contains trace ID, span ID, sampling decision
• baggage: Contains additional trace metadata

Configure Trace Propagation Targets

Only URLs matching these patterns receive trace headers:

Sentry.init({
  tracePropagationTargets: [
    "localhost",
    "https://api.yourapp.com",
    /^https:\/\/.*\.yourapp\.com\/api/,
  ],
});

Server-Side Rendering (Meta Tags)

For SSR apps, inject trace data in HTML:

// Server renders these meta tags
const traceData = Sentry.getTraceData();
// Include in HTML <head>:
// <meta name="sentry-trace" content="..." />
// <meta name="baggage" content="..." />

The browser SDK automatically reads these and continues the trace.

Manual Propagation

For non-HTTP channels (WebSockets, message queues):

// Sender
const traceData = Sentry.getTraceData();
sendMessage({
  ...payload,
  _traceHeaders: traceData,
});

// Receiver
Sentry.continueTrace(
  {
    sentryTrace: message._traceHeaders["sentry-trace"],
    baggage: message._traceHeaders["baggage"],
  },
  () => {
    processMessage(message);
  }
);

---

Common Operation Types

Use consistent op values for better organization:

Operation	Use Case
http.client	Outgoing HTTP requests
http.server	Incoming HTTP requests
db	Database operations
db.query	Database queries
cache	Cache operations
task	Background tasks
function	Function execution
ui.render	UI rendering
ui.action	User interactions
serialize	Serialization
middleware	Middleware execution

---

What Gets Automatically Traced

Browser (with browserTracingIntegration)

• Page loads
• Navigation/route changes
• XHR/fetch requests
• Long tasks
• Interaction to Next Paint (INP)

Next.js

• API routes
• Server components
• Page renders
• Data fetching

Node.js (with framework integrations)

• HTTP requests (Express, Fastify, etc.)
• Database queries (with ORM integrations)
• External API calls

Python (with framework integrations)

• Django views, middleware, templates
• Flask routes
• FastAPI endpoints
• SQLAlchemy queries
• Celery tasks

---

Disabling Tracing

Important: Setting tracesSampleRate: 0 does NOT disable tracing - it still processes traces but never sends them.

To fully disable tracing, omit both sampling options:

Sentry.init({
  dsn: "YOUR_DSN_HERE",
  // Do NOT include tracesSampleRate or tracesSampler
});

---

Production Sampling Recommendations

Traffic Level	Recommended Rate
Development/Testing	1.0 (100%)
Low traffic (<1K req/min)	0.5 - 1.0
Medium traffic (1K-10K req/min)	0.1 - 0.5
High traffic (>10K req/min)	0.01 - 0.1

Use dynamic sampling to capture more of important transactions:

tracesSampler: ({ name }) => {
  // Always capture errors and slow endpoints
  if (name.includes("checkout") || name.includes("payment")) {
    return 1.0;
  }
  // Sample most at 10%
  return 0.1;
},

---

Verification Steps

After setup, verify tracing is working:

JavaScript

// Trigger a test transaction
await Sentry.startSpan(
  { name: "test-transaction", op: "test" },
  async () => {
    console.log("Tracing test");
    await new Promise(resolve => setTimeout(resolve, 100));
  }
);

Python

with sentry_sdk.start_transaction(op="test", name="test-transaction"):
    print("Tracing test")

Check in Sentry:

1. Go to Performance section
2. Look for your test transaction
3. Verify spans appear in the trace waterfall

---

Common Issues and Solutions

Issue: Transactions not appearing

Solutions:

1. Verify tracesSampleRate > 0 or tracesSampler returns > 0
2. Check DSN is correct
3. For browser: Ensure browserTracingIntegration() is added
4. Wait a few minutes for data to process

Issue: Distributed traces not connected

Solutions:

1. Check tracePropagationTargets includes your API URLs
2. Verify CORS allows sentry-trace and baggage headers
3. For SSR: Ensure trace meta tags are rendered

Issue: Too many transactions (high volume)

Solutions:

1. Lower tracesSampleRate
2. Use tracesSampler to filter by transaction name
3. Use shouldCreateSpanForRequest to skip health checks

Issue: Spans not nested correctly

Solutions:

1. Ensure parent span is still active when creating child
2. Use startSpan callback pattern (not manual)
3. For browser: Consider parentSpanIsAlwaysRootSpan: false

---

Summary Checklist

## Sentry Tracing Setup Complete

### Configuration Applied:
- [ ] `tracesSampleRate` or `tracesSampler` configured
- [ ] Browser: `browserTracingIntegration()` added
- [ ] `tracePropagationTargets` configured for APIs
- [ ] Next.js App Router: `getTraceData()` in metadata

### Sampling Strategy:
- [ ] Development: 100% sampling for testing
- [ ] Production: Appropriate rate based on traffic

### Custom Instrumentation (if applicable):
- [ ] Critical paths instrumented with custom spans
- [ ] Consistent `op` values used

### Next Steps:
1. Trigger some requests in your application
2. Check Sentry > Performance for transactions
3. Review trace waterfalls for span hierarchy
4. Adjust sampling rates based on volume

---

Quick Reference

Platform	Enable Tracing	Custom Span
JS/Browser	tracesSampleRate + browserTracingIntegration()	Sentry.startSpan()
Next.js	tracesSampleRate (auto-integrated)	Sentry.startSpan()
Node.js	tracesSampleRate	Sentry.startSpan()
Python	traces_sample_rate	@sentry_sdk.trace or start_span()
Ruby	traces_sample_rate	start_span()

Sampling Option	Purpose
tracesSampleRate	Uniform percentage (0-1)
tracesSampler	Dynamic function (takes precedence)