TL;DR
For multi-domain testing: Use ExperimentHQ with cross-domain tracking. Key requirements: consistent user assignment across domains, shared cookies (via parent domain), and centralized experiment management. Test each domain separately unless you need cross-domain conversion tracking.
Multi-Domain Challenges
Cookie sharing
Solution: Use first-party cookies with shared parent domain
User consistency
Solution: Sync user ID across domains
Conversion attribution
Solution: Track cross-domain conversion paths
Centralized management
Solution: Single dashboard for all domains
Tool Comparison
| Tool | Cross-Domain | Central Management | Verdict |
|---|---|---|---|
| ExperimentHQ | Best Overall | ||
| VWO | Enterprise | ||
| Optimizely | Enterprise only |
Common Multi-Domain Scenarios
Marketing + App Domains
example.com (marketing) + app.example.com (product)
Multiple Brands
brand1.com, brand2.com under same company
Regional Sites
example.com, example.co.uk, example.de
Checkout on Different Domain
shop.example.com → checkout.example.com
Multi-Domain Testing
ExperimentHQ supports multi-domain tracking with consistent user assignment.