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PostHog analytics and feature flags setup
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| name | api-analytics-setup-posthog |
| description | PostHog analytics and feature flags setup |
Quick Guide: One-time setup for PostHog in Next.js App Router monorepo. Covers
posthog-jsclient provider,posthog-nodeserver client, environment variables, and Vercel deployment. PostHog handles both analytics AND feature flags with a generous free tier (1M events + 1M flag requests/month).
<critical_requirements>
All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering,
import type, named constants)
(You MUST use NEXT_PUBLIC_ prefix for client-side PostHog environment variables)
(You MUST create PostHogProvider as a 'use client' component - posthog-js requires browser APIs)
(You MUST call posthog.shutdown() or posthog.flush() after server-side event capture to prevent lost events)
(You MUST use defaults: '2025-11-30' or capture_pageview: 'history_change' for automatic SPA page tracking)
(You MUST use a single PostHog organization for all monorepo apps - projects are usage-based, not per-project pricing)
</critical_requirements>
Auto-detection: PostHog setup, posthog-js, posthog-node, PostHogProvider, analytics setup, feature flags setup, event tracking setup, NEXT_PUBLIC_POSTHOG_KEY
When to use:
When NOT to use:
backend/analytics.md for that)backend/feature-flags.md for that)Key patterns covered:
Detailed Resources:
PostHog is a product analytics + feature flags platform that consolidates multiple tools into one. It's open-source, can be self-hosted, and has a generous free tier. For solo developers and small teams, PostHog eliminates the need for separate analytics (Mixpanel/Amplitude) and feature flag (LaunchDarkly) services.
Core principles:
When to use PostHog:
When NOT to use PostHog:
Create a single PostHog organization for your monorepo. You can either use one project for all apps or create separate projects per app.
PostHog Organization: "Your Company"
├── Project: "Main App" (or separate per app)
│ ├── API Key: phc_xxx
│ └── Host: https://us.i.posthog.com (or eu.i.posthog.com)
# Example API key format
phc_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Why good: Single organization pools billing across all projects, 6 projects included on paid tier, usage-based pricing means you're not penalized for multiple apps
Install dependencies and configure for Next.js App Router.
# Install client-side SDK
bun add posthog-js
# apps/client-next/.env.local
# PostHog Configuration
NEXT_PUBLIC_POSTHOG_KEY=phc_your_project_api_key_here
NEXT_PUBLIC_POSTHOG_HOST=https://us.i.posthog.com
Next.js 15.3+: Use instrumentation-client.js (simpler, recommended)
Next.js < 15.3: Use PostHogProvider component (traditional approach)
See examples/core.md for both approaches with full implementation examples.
Why good: defaults: "2025-11-30" enables automatic SPA page/leave tracking, person_profiles: "identified_only" reduces event costs, debug mode in development aids troubleshooting
Install and configure the Node.js SDK for server-side event capture in API routes and Hono middleware.
# Install server-side SDK
bun add posthog-node
# apps/client-next/.env.local (or apps/server/.env.local)
# Server-side PostHog (no NEXT_PUBLIC_ prefix needed)
POSTHOG_API_KEY=phc_your_project_api_key_here
POSTHOG_HOST=https://us.i.posthog.com
Create a server client singleton for reuse across API routes. See examples/server.md for the full implementation including API route and Hono middleware examples.
Option 1: Use captureImmediate() - simplest, awaits HTTP request directly
Option 2: Use capture() + await flush() - batched, requires explicit flush
Why good: Singleton prevents multiple client instances, flushInterval/flushAt configure batching, shutdown function for graceful cleanup, captureImmediate for simple serverless usage
<critical_reminders>
All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering,
import type, named constants)
(You MUST use NEXT_PUBLIC_ prefix for client-side PostHog environment variables)
(You MUST create PostHogProvider as a 'use client' component - posthog-js requires browser APIs)
(You MUST call posthog.shutdown() or posthog.flush() after server-side event capture to prevent lost events)
(You MUST use defaults: '2025-11-30' or capture_pageview: 'history_change' for automatic SPA page tracking)
(You MUST use a single PostHog organization for all monorepo apps - projects are usage-based, not per-project pricing)
Failure to follow these rules will cause lost analytics events, broken tracking, or security vulnerabilities.
</critical_reminders>
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