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:

basic-integration-1.0-begin.md - PostHog Setup - Begin ← Start here
basic-integration-1.1-edit.md - PostHog Setup - Edit
basic-integration-1.2-revise.md - PostHog Setup - Revise
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)

Identifying users

Identify users during login and signup events. Refer to the example code and documentation for the correct identify pattern for this framework. If both frontend and backend code exist, pass the client-side session and distinct ID using X-POSTHOG-DISTINCT-ID and X-POSTHOG-SESSION-ID headers to maintain correlation.

Error tracking

Add PostHog error tracking to relevant files, particularly around critical user flows and API boundaries.