Best A/B Testing Tool for Authenticated Pages

TL;DR

For authenticated pages: Use PostHog, Statsig, or LaunchDarkly with user ID-based bucketing. This ensures same user sees same variant across devices and sessions. For marketing site (pre-login), use ExperimentHQ with cookie-based tracking.

Why Authenticated Pages Are Different

Key differences from public pages:

• User identity known: Can use account ID for bucketing
• Cross-device consistency: User logs in on phone and laptop
• Long-term tracking: Can track same user over weeks/months
• Privacy considerations: More sensitive data

Tool Comparison

Tool	Approach	Verdict
PostHog	User ID-based	Best for Product
Statsig	User ID-based	Best with Flags
LaunchDarkly	User ID-based	Best Feature Flags
ExperimentHQ	Cookie-based	Best for Marketing

Key Considerations

User-level consistency

Same user must always see same variant, even across devices

Account-based assignment

Use account ID, not session ID, for bucketing

Cross-device tracking

User logs in on mobile and desktop—should see same variant

Privacy

Ensure user data handling complies with your privacy policy

Implementation Pattern

// Pass user ID to A/B testing tool
const variant = experimentTool.getVariant({
  experimentId: 'onboarding-flow',
  userId: currentUser.id, // Use account ID, not session
})

// Render based on variant
if (variant === 'control') {
  return <OnboardingV1 />
} else {
  return <OnboardingV2 />
}

Choose Your Tool

For in-app experiments: PostHog or Statsig with user ID-based bucketing

For pre-login pages: ExperimentHQ with cookie-based tracking