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13 min read
What’s wild is how invisible it all is, it shows up in dashboards, reports, and headlines, yet almost nobody questions it. The Google Ads dashboard shows conversions, the Analytics report confirms the traffic, but the actual attribution path is often obscured by phantom sessions and broken identifiers. We accept the numbers, even though we know a significant chunk of customer journey data is disappearing silently into the digital ether.
Orla Gallagher
PPC & Paid Social Expert
Last Updated
November 20, 2025
The Problem: Cross-domain tracking breaks when Safari's ITP deletes cookies, causing attribution loss for multi-step customer journeys.
The Solution: Configure GTM Conversion Linker to preserve Google Click IDs in first-party cookies that survive ITP restrictions.
This Article Explains: What the Conversion Linker does, why it's necessary, complete step-by-step setup instructions, common configuration mistakes, and why it requires first-party infrastructure to work reliably.
Google Tag Manager Conversion Linker is a specialized tag that preserves Google Click IDs (GCLIDs) across pages and domains by storing them in first-party cookies. This enables accurate attribution when customers take multiple sessions or cross domain boundaries before converting.
The Conversion Linker solves three specific problems:
ITP cookie deletion - Safari automatically deletes tracking cookies after 7 days, breaking attribution for longer purchase cycles
Cross-domain tracking gaps - When customers move between domains (yoursite.com to checkout.yourdomain.com), cookies don't transfer automatically
GCLID parameter loss - URL parameters containing click information disappear on subsequent page loads without cookie storage
How it works:
User clicks Google Ad containing GCLID parameter
User lands on your website with GCLID in URL
Conversion Linker tag fires on page load
Tag reads GCLID from URL
Tag stores GCLID in first-party cookie on your domain
Cookie persists for 90 days (not subject to 7-day ITP limit)
Future conversions can be attributed to original ad click
Without Conversion Linker, the GCLID disappears after the landing page load. Multi-session purchases lose attribution because Google cannot connect the conversion back to the original ad click.
Standard Google Ads tracking fails in three scenarios that have become increasingly common due to browser privacy protections.
Apple's Intelligent Tracking Prevention monitors which domains set cookies. When it identifies tracking patterns, ITP applies aggressive expiration regardless of configured cookie lifespans.
Attribution breakdown timeline without Conversion Linker:
Day 1: User clicks Google Ad, lands on site with GCLID parameter
Day 1: Google Ads tag sets standard tracking cookie
Day 2-6: User researches, considers purchase
Day 7: Safari deletes tracking cookie (ITP 7-day limit)
Day 8: User returns to site to purchase
Day 8: Google Ads tag fires conversion event but has no cookie linking conversion to Day 1 click
Result: Conversion appears as "Direct" traffic instead of attributed to Google Ads
With Conversion Linker enabled:
Day 1: User clicks ad, Conversion Linker stores GCLID in first-party cookie
Day 7: Safari does not delete first-party cookie from your domain
Day 8: User converts, Google Ads tag reads GCLID from Conversion Linker cookie
Result: Conversion correctly attributed to Day 1 ad click
Many businesses use separate domains for different purposes:
Main site: yourcompany.com
Checkout: checkout.yourcompany.com or shop.yourdomain.com
Payment processing: pay.thirdparty.com
Cookies set on yourcompany.com cannot be read by checkout.yourcompany.com without special configuration. The GCLID stored in a cookie on the first domain is invisible to the second domain.
Standard tracking failure:
User clicks ad, lands on yourcompany.com
Cookie with GCLID set on yourcompany.com
User clicks "Buy Now," redirects to checkout.yourcompany.com
Checkout domain cannot read yourcompany.com cookies
Conversion fires without GCLID
Attribution lost
Conversion Linker solution:
User clicks ad, lands on yourcompany.com
Conversion Linker stores GCLID in cookie
Conversion Linker decorates link to checkout.yourcompany.com with _gl parameter
Checkout domain receives _gl parameter in URL
Conversion Linker on checkout domain reads _gl parameter
Conversion properly attributed
Modern customer journeys involve multiple sessions across days or weeks:
Session 1: Initial research from Google Ad click
Session 2: Comparison shopping (direct visit or bookmark)
Session 3: Final purchase decision (direct visit or email link)
Without persistent storage, only Session 1 has the GCLID. Sessions 2 and 3 have no connection to the original ad click unless a cookie preserves that information across sessions.
Setting up the Conversion Linker requires specific configuration in Google Tag Manager with attention to firing order and domain settings.
Navigate to GTM workspace:
Path: Tags > New > Tag Configuration
Tag Type: Select "Google Ads" from tag type list
Specific Tag: Choose "Conversion Linker"
Configuration options:
Enable cross-domain linking: Set to "True" if you track across multiple domains
Accept incoming linker parameters: Set to "True" to receive decorated URLs from other domains
Decorate outbound forms: Set to "True" if forms submit to external domains
Domain configuration:
If cross-domain tracking is enabled, you must specify domains:
Option 1: Select "Auto" to automatically detect
Option 2: Manually list domains: yoursite.com, checkout.yoursite.com, shop.yourdomain.com
Manual specification is more reliable than "Auto" for complex setups.
The Conversion Linker must fire on every page before other Google tags.
Trigger selection: Use "All Pages" trigger
Advanced settings: Configure tag sequencing
Setup tag: None (Conversion Linker runs first)
Cleanup tag: None
Firing priority: Set to higher number than other tags (e.g., 100)
Higher priority numbers fire first. If other Google tags have default priority (0), setting Conversion Linker to 100 ensures it executes before them.
For GDPR/CCPA compliance, configure consent requirements:
Path: Tag Configuration > Advanced Settings > Consent Settings
Required consent:
Ad Storage: Required (wait for user consent before firing)
Analytics Storage: Not required for Conversion Linker specifically
Consent initialization trigger:
If using consent management, change trigger from "All Pages" to "Consent Initialization - All Pages" to respect consent choices while still firing early in page load.
Test the configuration before publishing:
GTM Preview Mode:
Click "Preview" in GTM workspace
Enter your website URL
Click through to website with GTM debug panel active
Verify "Conversion Linker" tag fires on page load
Check firing order (should be first or among first tags)
Cookie verification:
Click a Google Ad or use test URL with gclid parameter
Open browser Developer Tools > Application > Cookies
Look for cookie named "_gcl_aw" under your domain
Verify cookie expiration is 90 days (not 7 days)
Close browser, return next day, verify cookie still exists
Cross-domain verification (if applicable):
Navigate to page with link to second domain
Click link and inspect URL of destination page
URL should contain "_gl=" parameter
Verify Conversion Linker tag fires on destination domain
Check that destination domain also has "_gcl_aw" cookie
After verification, publish the GTM container:
Publish process:
Click "Submit" in GTM
Add version name: "Added Conversion Linker configuration"
Add description detailing changes
Click "Publish"
Post-launch monitoring:
Monitor Google Ads conversion tracking for 7-14 days:
Check attribution source reports
Compare "Direct" conversion percentage before and after
Verify conversions occurring 7+ days after ad click are properly attributed
Monitor cross-domain conversion attribution if applicable
Several configuration errors prevent Conversion Linker from working correctly.
If Google Ads Conversion tags or GA4 tags fire before the Conversion Linker, they may not have access to the stored GCLID.
Problem indicator: Conversions tracked but not attributed to campaigns
Solution: Set Conversion Linker firing priority higher than all other tags (priority 100 vs. default 0)
Verification: In GTM Preview, check Tags Fired sequence and confirm Conversion Linker appears first
Cross-domain tracking fails when domain lists are incomplete or incorrectly formatted.
Common errors:
Including "https://" in domain list (wrong: https://yoursite.com, correct: yoursite.com)
Missing subdomains (need both yoursite.com and shop.yoursite.com)
Forgetting staging or test environments (test.yoursite.com)
Solution: List all domains and subdomains in plain format without protocol
Test: Navigate between all listed domains and verify "_gl=" parameter appears in URLs
If Conversion Linker exists on Domain A but not Domain B, the link decoration works but Domain B cannot read and store the parameter.
Problem: User clicks from yoursite.com (has Conversion Linker) to checkout.yoursite.com (no Conversion Linker)
Result: _gl parameter arrives in URL but is never processed into a cookie
Solution: Deploy identical Conversion Linker configuration to all domains involved in conversion path
The most fundamental problem occurs when the GTM container itself never loads due to ad blocker filtering.
Problem: uBlock Origin blocks googletagmanager.com
Result: No GTM tags fire, including Conversion Linker
Impact: 20-30% of traffic has zero tracking or attribution
Diagnosis: Check GTM firing statistics for unusually low trigger counts relative to actual traffic
Even with correct configuration, the Conversion Linker has limitations that cause attribution gaps.
Ad blockers identify googletagmanager.com as a tracking domain and prevent the script from loading. If the GTM container never loads, no tags inside it can execute.
Affected traffic percentage: 20-40% depending on audience
Browsers affected: All browsers with ad blocker extensions
Privacy browsers affected: Brave (built-in blocking), Firefox with strict tracking protection
Solution required: Load GTM from first-party subdomain via CNAME configuration
When checkout redirects to external payment processors (Stripe hosted checkout, PayPal, Square), the conversion occurs on a domain you don't control.
Problem scenario:
User starts checkout on yoursite.com (has Conversion Linker)
Redirects to checkout.stripe.com for payment
Purchase completes on checkout.stripe.com
You cannot install GTM on Stripe's domain
Conversion fires without GCLID access
Solutions:
Use embedded payment forms that keep user on your domain
Implement server-side conversion tracking that captures GCLID before redirect
Use Stripe's metadata fields to pass GCLID through payment process
Links within iframes or third-party widgets may not be decorated by the Conversion Linker.
Common scenarios:
Chat widgets with "Buy Now" links
Embedded product configurators
Payment form iframes
Technical reason: JavaScript in parent page cannot access or modify content inside cross-origin iframes for security reasons
Solution: Work with widget vendors to support link decoration or move critical conversion paths outside iframes
The Conversion Linker's effectiveness depends entirely on the GTM container loading reliably. First-party architecture solves the blocking problem.
Instead of loading GTM from googletagmanager.com, configure it to load from your subdomain.
Traditional setup:
<script src="https://www.googletagmanager.com/gtm.js?id=GTM-XXXXX"></script>
First-party setup:
Create subdomain: gtm.yourcompany.com
Configure CNAME DNS record: gtm.yourcompany.com → googletagmanager.com
Update GTM script reference to use subdomain
Browser perspective:
Request goes to gtm.yourcompany.com (your domain)
Ad blockers check filter lists
Your subdomain not on third-party tracking lists
Request allowed, GTM loads successfully
This ensures Conversion Linker always fires because the containing GTM script always loads.
Server-Side Google Tag Manager moves tag execution from browser to your server, making it immune to client-side blocking.
Architecture:
Client-side GTM (with Conversion Linker) captures GCLID and stores in cookie
Client-side GTM sends event data to your server-side GTM container
Server-side GTM reads GCLID from event data
Server-side GTM forwards conversion with GCLID to Google Ads via server API
Attribution succeeds regardless of client-side blocking
Conversion Linker role in SSGTM:
The client-side Conversion Linker remains essential because it captures the GCLID from the URL and makes it available for server-side processing. Without it, server-side GTM has no GCLID to work with.
Advanced implementations use comprehensive first-party collectors that handle all identifier preservation automatically.
Traditional approach:
GTM Conversion Linker for Google identifiers (GCLID)
Meta Pixel for Facebook identifiers (FBC, FBP)
Separate scripts for other platforms
Each platform has independent identifier management
Unified first-party approach:
Single script from CNAME subdomain
Automatically captures all platform identifiers (GCLID, FBC, UTM parameters)
Stores in unified first-party cookie structure
Distributes to all platforms via server-side connections
This approach provides the benefits of Conversion Linker for all platforms simultaneously, not just Google.
Several approaches achieve similar attribution preservation with different trade-offs.
Enhanced Conversions uses hashed customer data (email, phone) to match conversions to clicks instead of relying solely on cookies.
How it works:
Customer submits email during checkout
Website hashes email with SHA256
Hashed email sent to Google with conversion
Google matches hashed email to ad click in their system
Advantages:
Works when cookies are deleted
More privacy-preserving
Compatible with consent restrictions
Limitations:
Only works for logged-in or form-submitting users
Requires customer data collection and handling
Less precise than cookie-based matching
Relationship to Conversion Linker: Use both together for maximum attribution accuracy
Capture conversion data on your server and send directly to Google Ads API, bypassing browser entirely.
Implementation:
Customer completes purchase
Your e-commerce platform records transaction
Server-side script sends conversion event to Google Ads API
Include GCLID captured earlier (stored in database or session)
Advantages:
Not affected by ad blockers
Not affected by ITP
Reliable delivery guaranteed
Limitations:
Requires significant development
Must implement GCLID storage and retrieval system
More complex debugging
Comprehensive platforms like DataCops provide unified identifier management across all marketing platforms.
Capabilities:
CNAME-based collection immune to ad blocker filtering
Automatic capture of all marketing identifiers (GCLID, FBC, UTM)
Persistent first-party cookies surviving ITP restrictions
Server-side distribution to all ad platforms
Real-time bot filtering
Advantages over standalone Conversion Linker:
Works for all platforms (Google, Meta, TikTok, etc.)
Includes fraud filtering
Integrated consent management
Single implementation covering all needs
DataCops provides comprehensive first-party data collection that includes all functionality of the Conversion Linker while extending it to all marketing platforms. The platform operates from your subdomain via CNAME configuration, ensuring tracking scripts load regardless of ad blocker status.
Automatic capture of Google Click IDs, Facebook Click IDs, UTM parameters, and other marketing identifiers occurs on every page load. These identifiers are stored in persistent first-party cookies that survive Safari's ITP restrictions.
Server-side distribution sends complete attribution data to Google Ads Measurement Protocol, Meta Conversion API, and other platforms via unblockable API connections. This ensures conversions are attributed correctly even when client-side pixels are blocked.
The system eliminates the need for separate Conversion Linker configuration by integrating identifier preservation into the core collection infrastructure, while simultaneously adding bot filtering and consent management capabilities.
The Google Tag Manager Conversion Linker is essential for accurate Google Ads attribution when customers take multiple sessions or cross domains before converting. Proper configuration requires firing on all pages before other tags, correct domain specification, and verification across browsers.
However, the Conversion Linker cannot function if the GTM container itself gets blocked by ad blockers. This affects 20-40% of traffic. First-party infrastructure via CNAME configuration solves this by making GTM load from your own domain, ensuring the Conversion Linker always fires.
For complete attribution infrastructure covering all marketing platforms (not just Google), unified first-party collection provides the Conversion Linker's benefits while extending them to Meta, TikTok, and other platforms, with added fraud filtering and consent management. This is the complete solution for modern attribution requirements.