Introduction
A forex broker ran a web setup across multiple domains: their marketing site, blog, support centre, and an account portal. Heavy affiliate traffic created a mess of additional domains. Google Tag Manager (GTM) started pulling in data from many external domains, which threatened to corrupt their tracking and mess up data quality.
The solution: Deploy a Conversion Linker tag with a regex-based filter that only fires on approved hostnames. This kept cookie linking and cross-domain attribution working properly across verified company properties only.
Background
The platform’s web ecosystem included:
Primary site: abc.com – primary client website for all users.
Blog: abc-blog.com – hosted for optimal SEO
Support centre: abc-help.com – operated under a subdomain for assistance.
Login portal: abc-login.com- a portal dedicated to authenticating returning users.
Additionally, the affiliate traffic made everything messier. GTM’s Overview panel started showing an endless list of irrelevant hostnames. Without proper controls, the Conversion Linker could fire on domains they didn’t own, creating attribution errors, reliability issues, and privacy risks.
Project Goals
- Restrict Tag Execution to Company-Owned Domains: Keep Conversion Linker triggering limited only to verified domains.
- Streamline Domain Management: Use regex to handle current and future subdomains.
- Preserve Cross-Domain Attribution: Keep user journey tracking consistent between all domains and subdomains in GA4.
- Eliminate Noise from Affiliate & Third-Party Domains: Stop tags from firing on affiliate tracking pages or embedded iframes outside the verified domains.
- Improve Analytics Accuracy: Get cleaner data with reliable attribution, and eliminate contamination from unrelated referral sources.
Implementation Steps
- Domain Inventory & Verification: With the assistance of the development team, we created a list of verified client-owned domains and subdomains across all environments.
- Regex Pattern for Permitted Hostnames: Using the acquired list of verified domains, we built a consolidated regex pattern using GTM’s {{Page Hostname}} variable to match all authorised domains within a single rule, making it more scalable.
- Conversion Linker Tag Configuration:
- Set up the Conversion Linker to:
- Auto Link Domains across verified properties.
- Trigger on Permitted Hostnames using the regex pattern, so that it only activates on client-owned sites.
- Affiliate Exclusion: Explicitly blocked any external or unverified domains using the regex, preventing cookie linking outside the client-owned domains.
- Testing & Validation
- Used GTM Preview Mode and GA4 DebugView to confirm:
- The conversion linker tag is triggered only when the hostname matches the regex pattern.
- Proper and accurate tracking between all domains and subdomains.
- No tag activation on any of the affiliated or third-party sites.
Results and Benefits
- Strict Domain Control – The conversion linker tag only triggered on verified domains belonging to the client.
- Future-Proof Architecture – Using regex for the page hostname trigger allowed the addition of future domains much more easily.
- Enhanced Attribution – With enhanced attribution, users are tracked seamlessly while transitioning between multiple domains.
- Data Integrity – Ensured that no other third-party embeds or affiliates are contaminating the data.
- Reduced Maintenance – Using a single regex rule over the trigger helped cut GTM maintenance work by avoiding the manual, long list of domains.
Conclusion
The regex-based permitted hostname setup protected the Conversion Linker from firing on unauthorised domains. This kept cross-domain attribution accurate and simplified GTM management.
Due to this solution, our client can now benefit from clean GA4 attribution and separated affiliate data. This implementation also made future scaling straightforward, allowing the client to now focus on precise performance tracking with minimal operational hassle.
