Posthog Analytics

PostHog Analytics Skill

For implementing product analytics with PostHog - event tracking, user identification, feature flags, and project-specific dashboards.

Sources: PostHog Docs | Product Analytics | Feature Flags

Philosophy

Measure what matters, not everything.

Analytics should answer specific questions:

• Are users getting value? (activation, retention)
• Where do users struggle? (funnels, drop-offs)
• What features drive engagement? (feature usage)
• Is the product growing? (acquisition, referrals)

Don't track everything. Track what informs decisions.

Installation

Next.js (App Router)

npm install posthog-js

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

export function initPostHog() {
  if (typeof window !== 'undefined' && !posthog.__loaded) {
    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', // Only create profiles for identified users
      capture_pageview: false, // We'll handle this manually for SPA
      capture_pageleave: true,
      loaded: (posthog) => {
        if (process.env.NODE_ENV === 'development') {
          posthog.debug();
        }
      },
    });
  }
  return posthog;
}

export { posthog };

// app/providers.tsx
'use client';

import { useEffect } from 'react';
import { usePathname, useSearchParams } from 'next/navigation';
import { initPostHog, posthog } from '@/lib/posthog';

export function PostHogProvider({ children }: { children: React.ReactNode }) {
  const pathname = usePathname();
  const searchParams = useSearchParams();

  useEffect(() => {
    initPostHog();
  }, []);

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

  return <>{children}</>;
}

// app/layout.tsx
import { PostHogProvider } from './providers';

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

React (Vite/CRA)

// src/posthog.ts
import posthog from 'posthog-js';

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

export { posthog };

// src/main.tsx
import { PostHogProvider } from 'posthog-js/react';
import { posthog } from './posthog';

ReactDOM.createRoot(document.getElementById('root')!).render(
  <PostHogProvider client={posthog}>
    <App />
  </PostHogProvider>
);

Python (FastAPI/Flask)

pip install posthog

# analytics/posthog_client.py
import posthog
from functools import lru_cache

@lru_cache()
def get_posthog():
    posthog.project_api_key = os.environ["POSTHOG_API_KEY"]
    posthog.host = os.environ.get("POSTHOG_HOST", "https://us.i.posthog.com")
    posthog.debug = os.environ.get("ENV") == "development"
    return posthog

# Usage
def track_event(user_id: str, event: str, properties: dict = None):
    ph = get_posthog()
    ph.capture(
        distinct_id=user_id,
        event=event,
        properties=properties or {}
    )

def identify_user(user_id: str, properties: dict):
    ph = get_posthog()
    ph.identify(user_id, properties)

Node.js (Express/Hono)

npm install posthog-node

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

const posthog = new PostHog(process.env.POSTHOG_API_KEY!, {
  host: process.env.POSTHOG_HOST || 'https://us.i.posthog.com',
});

// Flush on shutdown
process.on('SIGTERM', () => posthog.shutdown());

export { posthog };

// Usage
export function trackEvent(userId: string, event: string, properties?: Record<string, any>) {
  posthog.capture({
    distinctId: userId,
    event,
    properties,
  });
}

export function identifyUser(userId: string, properties: Record<string, any>) {
  posthog.identify({
    distinctId: userId,
    properties,
  });
}

Environment Variables

# .env.local (Next.js) - SAFE: These are meant to be public
NEXT_PUBLIC_POSTHOG_KEY=phc_xxxxxxxxxxxxxxxxxxxx
NEXT_PUBLIC_POSTHOG_HOST=https://us.i.posthog.com

# .env (Backend) - Keep private
POSTHOG_API_KEY=phc_xxxxxxxxxxxxxxxxxxxx
POSTHOG_HOST=https://us.i.posthog.com

Add to credentials.md patterns:

'POSTHOG_API_KEY': r'phc_[A-Za-z0-9]+',

User Identification

When to Identify

// Identify on signup
async function handleSignup(email: string, name: string) {
  const user = await createUser(email, name);

  posthog.identify(user.id, {
    email: user.email,
    name: user.name,
    created_at: user.createdAt,
    plan: 'free',
  });

  posthog.capture('user_signed_up', {
    signup_method: 'email',
  });
}

// Identify on login
async function handleLogin(email: string) {
  const user = await authenticateUser(email);

  posthog.identify(user.id, {
    email: user.email,
    name: user.name,
    plan: user.plan,
    last_login: new Date().toISOString(),
  });

  posthog.capture('user_logged_in');
}

// Reset on logout
function handleLogout() {
  posthog.capture('user_logged_out');
  posthog.reset(); // Clears identity
}

User Properties

// Standard properties to track
interface UserProperties {
  // Identity
  email: string;
  name: string;

  // Lifecycle
  created_at: string;
  plan: 'free' | 'pro' | 'enterprise';

  // Engagement
  onboarding_completed: boolean;
  feature_count: number;

  // Business
  company_name?: string;
  company_size?: string;
  industry?: string;
}

// Update properties when they change
posthog.capture('$set', {
  $set: { plan: 'pro' },
});

Event Tracking Patterns

Event Naming Convention

// Format: [object]_[action]
// Use snake_case, past tense for actions

// ✅ Good event names
'user_signed_up'
'feature_created'
'subscription_upgraded'
'onboarding_completed'
'invite_sent'
'file_uploaded'
'search_performed'
'checkout_started'
'payment_completed'

// ❌ Bad event names
'click'           // Too vague
'ButtonClick'     // Not snake_case
'user signup'     // Spaces
'creatingFeature' // Not past tense

Core Events by Category

// === AUTHENTICATION ===
posthog.capture('user_signed_up', {
  signup_method: 'google' | 'email' | 'github',
  referral_source: 'organic' | 'paid' | 'referral',
});

posthog.capture('user_logged_in', {
  login_method: 'google' | 'email' | 'magic_link',
});

posthog.capture('user_logged_out');

posthog.capture('password_reset_requested');

// === ONBOARDING ===
posthog.capture('onboarding_started');

posthog.capture('onboarding_step_completed', {
  step_name: 'profile' | 'preferences' | 'first_action',
  step_number: 1,
  total_steps: 3,
});

posthog.capture('onboarding_completed', {
  duration_seconds: 120,
  steps_skipped: 0,
});

posthog.capture('onboarding_skipped', {
  skipped_at_step: 2,
});

// === FEATURE USAGE ===
posthog.capture('feature_used', {
  feature_name: 'export' | 'share' | 'duplicate',
  context: 'dashboard' | 'editor',
});

posthog.capture('[resource]_created', {
  resource_type: 'project' | 'document' | 'team',
  // Resource-specific properties
});

posthog.capture('[resource]_updated', {
  resource_type: 'project',
  fields_changed: ['name', 'description'],
});

posthog.capture('[resource]_deleted', {
  resource_type: 'project',
});

// === BILLING ===
posthog.capture('pricing_page_viewed', {
  current_plan: 'free',
});