add-analytics

Wire PostHog analytics, Sentry error tracking, and a health endpoint into any web project. Reads your stack, installs the right packages, and instruments your app so you stop flying blind in production.

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Install skill "add-analytics" with this command: npx skills add tushaarmehtaa/tushar-skills/tushaarmehtaa-tushar-skills-add-analytics

Wire observability into any web project. This skill adds event tracking, error monitoring, and a status endpoint — the three things every indie builder says they'll add later but never does.

Phase 1: Detect the Stack

Read the project and figure out what to install.

1.1 Framework

  • next.config.* → Next.js (check App Router vs Pages Router)
  • vite.config.* → Vite / React SPA
  • astro.config.* → Astro
  • nuxt.config.* → Nuxt
  • Python backend (main.py, app.py, manage.py) → FastAPI / Django / Flask

1.2 Existing Analytics

Check if any analytics/monitoring is already installed:

  • posthog-js or posthog-node → PostHog already present
  • @sentry/nextjs or @sentry/react or sentry-sdk → Sentry already present
  • @vercel/analytics → Vercel Analytics present
  • @google-analytics or gtag → GA present

If already installed, audit the setup instead of installing fresh. Check for gaps (missing error boundaries, no server-side tracking, no health endpoint).

1.3 Ask the User

Detected: [framework]
Existing analytics: [what's already there, or "none"]

I'll set up:
1. PostHog — event tracking, user identification, feature flags
2. Sentry — error tracking with source maps
3. Health endpoint — /api/status for uptime monitoring

Need your project keys:
- PostHog API key (get from app.posthog.com → Project Settings)
- Sentry DSN (get from sentry.io → Project Settings → Client Keys)

Or I can set up the code and you add the keys later.

Phase 2: PostHog Analytics

2.1 Install

Next.js:

npm install posthog-js posthog-node

React SPA (Vite):

npm install posthog-js

Python:

pip install posthog

2.2 Client-Side Provider

Next.js App Router — create app/providers.tsx:

'use client';

import posthog from 'posthog-js';
import { PostHogProvider as PHProvider, usePostHog } from 'posthog-js/react';
import { useEffect } from 'react';

if (typeof window !== 'undefined' && process.env.NEXT_PUBLIC_POSTHOG_KEY) {
  posthog.init(process.env.NEXT_PUBLIC_POSTHOG_KEY, {
    api_host: process.env.NEXT_PUBLIC_POSTHOG_HOST || 'https://us.i.posthog.com',
    person_profiles: 'identified_only',
    capture_pageview: false, // We handle this manually for SPA navigation
    capture_pageleave: true,
    loaded: (posthog) => {
      if (process.env.NODE_ENV === 'development') {
        // Disable in dev unless you want to test
        // posthog.opt_out_capturing();
      }
    },
  });
}

export function PostHogProvider({ children }: { children: React.ReactNode }) {
  return <PHProvider client={posthog}>{children}</PHProvider>;
}

Wrap the app in layout.tsx:

import { PostHogProvider } from './providers';

export default function RootLayout({ children }: { children: React.ReactNode }) {
  return (
    <html>
      <body>
        <PostHogProvider>{children}</PostHogProvider>
      </body>
    </html>
  );
}

React SPA (Vite) — create lib/analytics.ts:

import posthog from 'posthog-js';

let initialized = false;

export function initAnalytics() {
  if (initialized || typeof window === 'undefined') return;

  const key = import.meta.env.VITE_POSTHOG_KEY;
  if (!key) return;

  posthog.init(key, {
    api_host: import.meta.env.VITE_POSTHOG_HOST || 'https://us.i.posthog.com',
    person_profiles: 'identified_only',
    capture_pageview: true,
  });

  initialized = true;
}

export { posthog };

Call initAnalytics() in your app entry point.

2.3 Page View Tracking (Next.js SPA)

PostHog doesn't auto-track SPA navigation. Add a component that fires on route changes:

// components/PostHogPageView.tsx
'use client';

import { usePathname, useSearchParams } from 'next/navigation';
import { usePostHog } from 'posthog-js/react';
import { useEffect, Suspense } from 'react';

function PageViewTracker() {
  const pathname = usePathname();
  const searchParams = useSearchParams();
  const posthog = usePostHog();

  useEffect(() => {
    if (pathname && posthog) {
      let url = window.origin + pathname;
      const search = searchParams.toString();
      if (search) url += '?' + search;
      posthog.capture('$pageview', { $current_url: url });
    }
  }, [pathname, searchParams, posthog]);

  return null;
}

export function PostHogPageView() {
  return (
    <Suspense fallback={null}>
      <PageViewTracker />
    </Suspense>
  );
}

Add to layout:

<PostHogProvider>
  <PostHogPageView />
  {children}
</PostHogProvider>

2.4 User Identification

When a user logs in, identify them in PostHog so events are linked to a person:

import posthog from 'posthog-js';

// Call this after successful auth sync
function identifyUser(user: { id: string; email?: string; name?: string }) {
  posthog.identify(user.id, {
    email: user.email,
    name: user.name,
  });
}

// Call this on logout
function resetUser() {
  posthog.reset();
}

Wire this into your auth hook or auth sync callback.

2.5 Custom Event Tracking

Create a thin wrapper for type safety and consistency:

// lib/track.ts
import posthog from 'posthog-js';

type TrackEvent =
  | { event: 'signed_up'; properties?: { method: string } }
  | { event: 'created_project'; properties: { projectId: string } }
  | { event: 'upgraded_plan'; properties: { plan: string; price: number } }
  | { event: 'used_feature'; properties: { feature: string } };

export function track({ event, properties }: TrackEvent) {
  posthog.capture(event, properties);
}

Usage:

track({ event: 'created_project', properties: { projectId: '123' } });

The union type ensures you can't track events with wrong properties. Add your events to the union as your product grows.

2.6 Server-Side Tracking (Next.js)

For events that happen on the server (API routes, webhooks):

// lib/posthog-server.ts
import { PostHog } from 'posthog-node';

let client: PostHog | null = null;

export function getPostHogServer() {
  if (!client && process.env.POSTHOG_API_KEY) {
    client = new PostHog(process.env.POSTHOG_API_KEY, {
      host: process.env.NEXT_PUBLIC_POSTHOG_HOST || 'https://us.i.posthog.com',
      flushAt: 1,
      flushInterval: 0,
    });
  }
  return client;
}

Usage in API routes:

const posthog = getPostHogServer();
posthog?.capture({
  distinctId: userId,
  event: 'api_call',
  properties: { endpoint: '/api/generate', status: 200 },
});

Phase 3: Sentry Error Tracking

3.1 Install

Next.js:

npx @sentry/wizard@latest -i nextjs

This auto-creates sentry.client.config.ts, sentry.server.config.ts, sentry.edge.config.ts, and updates next.config.ts. Review the generated files.

React SPA (Vite):

npm install @sentry/react

Python (FastAPI):

pip install sentry-sdk[fastapi]

3.2 Configuration

Next.js — the wizard generates most of this. Review and adjust:

sentry.client.config.ts:

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

Sentry.init({
  dsn: process.env.NEXT_PUBLIC_SENTRY_DSN,
  tracesSampleRate: process.env.NODE_ENV === 'production' ? 0.1 : 1.0,
  replaysSessionSampleRate: 0,
  replaysOnErrorSampleRate: 1.0,
  debug: false,
  enabled: process.env.NODE_ENV === 'production',
});

Key settings:

  • tracesSampleRate: 0.1 — sample 10% of transactions in prod (controls cost)
  • replaysOnErrorSampleRate: 1.0 — always capture session replay when errors happen
  • enabled: false in development — don't pollute Sentry with dev errors

React SPA:

import * as Sentry from '@sentry/react';

Sentry.init({
  dsn: import.meta.env.VITE_SENTRY_DSN,
  integrations: [
    Sentry.browserTracingIntegration(),
    Sentry.replayIntegration(),
  ],
  tracesSampleRate: 0.1,
  replaysSessionSampleRate: 0,
  replaysOnErrorSampleRate: 1.0,
  enabled: import.meta.env.PROD,
});

Python (FastAPI):

import sentry_sdk

sentry_sdk.init(
    dsn=os.getenv("SENTRY_DSN"),
    traces_sample_rate=0.1,
    profiles_sample_rate=0.1,
    environment=os.getenv("ENVIRONMENT", "development"),
    enabled=os.getenv("ENVIRONMENT") == "production",
)

3.3 Error Boundary (React)

Create a global error boundary that catches rendering errors:

Next.js App Router — app/global-error.tsx:

'use client';

import * as Sentry from '@sentry/nextjs';
import { useEffect } from 'react';

export default function GlobalError({
  error,
  reset,
}: {
  error: Error & { digest?: string };
  reset: () => void;
}) {
  useEffect(() => {
    Sentry.captureException(error);
  }, [error]);

  return (
    <html>
      <body>
        <div style={{ padding: '2rem', textAlign: 'center' }}>
          <h1>something went wrong</h1>
          <p style={{ color: '#666', marginTop: '0.5rem' }}>
            the error has been reported automatically.
          </p>
          <button
            onClick={reset}
            style={{ marginTop: '1rem', padding: '0.5rem 1rem', cursor: 'pointer' }}
          >
            try again
          </button>
        </div>
      </body>
    </html>
  );
}

Also add app/error.tsx for non-fatal page errors:

'use client';

import * as Sentry from '@sentry/nextjs';
import { useEffect } from 'react';

export default function Error({
  error,
  reset,
}: {
  error: Error & { digest?: string };
  reset: () => void;
}) {
  useEffect(() => {
    Sentry.captureException(error);
  }, [error]);

  return (
    <div style={{ padding: '2rem' }}>
      <h2>something went wrong</h2>
      <button onClick={reset}>try again</button>
    </div>
  );
}

3.4 Structured Error Logging

Create a helper for logging errors with context:

// lib/logger.ts
import * as Sentry from '@sentry/nextjs';

interface ErrorContext {
  userId?: string;
  action?: string;
  metadata?: Record<string, any>;
}

export function logError(error: unknown, context?: ErrorContext) {
  const err = error instanceof Error ? error : new Error(String(error));

  if (context) {
    Sentry.withScope((scope) => {
      if (context.userId) scope.setUser({ id: context.userId });
      if (context.action) scope.setTag('action', context.action);
      if (context.metadata) scope.setExtras(context.metadata);
      Sentry.captureException(err);
    });
  } else {
    Sentry.captureException(err);
  }

  // Also log to console in development
  if (process.env.NODE_ENV !== 'production') {
    console.error('[Error]', err.message, context);
  }
}

Usage:

try {
  await generateContent(prompt);
} catch (error) {
  logError(error, {
    userId: user.id,
    action: 'generate_content',
    metadata: { promptLength: prompt.length },
  });
}

Phase 4: Health Endpoint

A single endpoint that tells you if the app is alive. Use it for uptime monitoring (Vercel cron, UptimeRobot, Better Uptime).

Next.js — app/api/status/route.ts:

import { NextResponse } from 'next/server';

const startTime = Date.now();

export async function GET() {
  const uptime = Math.floor((Date.now() - startTime) / 1000);

  // Basic health check
  const health: Record<string, any> = {
    status: 'ok',
    uptime: `${uptime}s`,
    timestamp: new Date().toISOString(),
    environment: process.env.NODE_ENV || 'unknown',
    version: process.env.NEXT_PUBLIC_APP_VERSION || 'dev',
  };

  // Database check (if applicable)
  try {
    // Supabase
    if (process.env.NEXT_PUBLIC_SUPABASE_URL) {
      const { createClient } = await import('@supabase/supabase-js');
      const supabase = createClient(
        process.env.NEXT_PUBLIC_SUPABASE_URL,
        process.env.SUPABASE_SERVICE_ROLE_KEY!
      );
      const { error } = await supabase.from('users').select('id').limit(1);
      health.database = error ? 'error' : 'ok';
    }

    // Prisma
    // const count = await prisma.user.count();
    // health.database = 'ok';
  } catch {
    health.database = 'error';
  }

  const isHealthy = health.database !== 'error';

  return NextResponse.json(health, {
    status: isHealthy ? 200 : 503,
  });
}

Python (FastAPI):

from datetime import datetime
import time

START_TIME = time.time()

@app.get("/api/status")
async def health_check():
    uptime = int(time.time() - START_TIME)
    return {
        "status": "ok",
        "uptime": f"{uptime}s",
        "timestamp": datetime.utcnow().isoformat(),
        "environment": os.getenv("ENVIRONMENT", "development"),
    }

What to monitor

Set up a cron or external service to hit /api/status every 5 minutes. Alert if:

  • Response status is not 200
  • Response time exceeds 5 seconds
  • Database field is "error"

Free options: UptimeRobot (free tier), Better Uptime, or Vercel's built-in cron.

Phase 5: Environment Variables

Add to .env.local (or .env):

# PostHog
NEXT_PUBLIC_POSTHOG_KEY=phc_...
NEXT_PUBLIC_POSTHOG_HOST=https://us.i.posthog.com
POSTHOG_API_KEY=phc_...  # Same key, used server-side

# Sentry
NEXT_PUBLIC_SENTRY_DSN=https://xxx@o123.ingest.sentry.io/456
SENTRY_AUTH_TOKEN=sntrys_...  # For source map uploads
SENTRY_ORG=your-org
SENTRY_PROJECT=your-project

Verify none of these are committed to git. Check .gitignore includes .env*.

Phase 6: Verify

After wiring everything, test each system:

PostHog:
[ ] Open the app → check PostHog dashboard for a pageview event
[ ] Navigate between pages → each page triggers a pageview
[ ] Log in → user appears in PostHog with email/name (identified)
[ ] Track a custom event → appears in PostHog events
[ ] Log out → posthog.reset() called, new anonymous session

Sentry:
[ ] Add a temporary `throw new Error('sentry test')` to a page
[ ] Load the page → error appears in Sentry dashboard
[ ] Check that source maps resolve (you see your actual code, not minified)
[ ] Remove the test error
[ ] Error boundary renders fallback UI (not a white screen)

Health Endpoint:
[ ] GET /api/status returns 200 with uptime and database status
[ ] If database is down, returns 503
[ ] Set up monitoring service to ping it every 5 minutes

Tell the user which systems are live and working.

Important Notes

  • PostHog is free up to 1M events/month. More than enough for indie projects.
  • Sentry is free up to 5K errors/month. If you're hitting that, you have bigger problems.
  • Don't track PII in PostHog events (no passwords, no credit card numbers). User IDs and emails are fine.
  • Sample rates matter. 10% tracing in prod keeps costs near zero. Increase only if debugging specific issues.
  • Source maps are critical for Sentry. Without them, error stack traces show minified code. The Sentry wizard handles this for Next.js. For other frameworks, upload maps during build.

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