integration-nextjs-app-router

PostHog integration for Next.js App Router

This skill helps you add PostHog analytics to Next.js App Router applications.

Workflow

Follow these steps in order to complete the integration:

1. basic-integration-1.0-begin.md - PostHog Setup - Begin ← Start here
2. basic-integration-1.1-edit.md - PostHog Setup - Edit
3. basic-integration-1.2-revise.md - PostHog Setup - Revise
4. basic-integration-1.3-conclude.md - PostHog Setup - Conclusion

Reference files

• references/EXAMPLE.md - Next.js App Router example project code
• references/next-js.md - Next.js - docs
• references/identify-users.md - Identify users - docs
• references/basic-integration-1.0-begin.md - PostHog setup - begin
• references/basic-integration-1.1-edit.md - PostHog setup - edit
• references/basic-integration-1.2-revise.md - PostHog setup - revise
• references/basic-integration-1.3-conclude.md - PostHog setup - conclusion

The example project shows the target implementation pattern. Consult the documentation for API details.

Key principles

• Environment variables: Always use environment variables for PostHog keys. Never hardcode them.
• Minimal changes: Add PostHog code alongside existing integrations. Don't replace or restructure existing code.
• Match the example: Your implementation should follow the example project's patterns as closely as possible.

Framework guidelines

• For Next.js 15.3+, initialize PostHog in instrumentation-client.ts for the simplest setup
• For feature flags, use useFeatureFlagEnabled() or useFeatureFlagPayload() hooks - they handle loading states and external sync automatically
• Add analytics capture in event handlers where user actions occur, NOT in useEffect reacting to state changes
• Do NOT use useEffect for data transformation - calculate derived values during render instead
• Do NOT use useEffect to respond to user events - put that logic in the event handler itself
• Do NOT use useEffect to chain state updates - calculate all related updates together in the event handler
• Do NOT use useEffect to notify parent components - call the parent callback alongside setState in the event handler
• To reset component state when a prop changes, pass the prop as the component's key instead of using useEffect
• useEffect is ONLY for synchronizing with external systems (non-React widgets, browser APIs, network subscriptions)
• When a reverse proxy is configured, both /static/* AND /array/* must route to the assets origin (us-assets.i.posthog.com or eu-assets.i.posthog.com).