A real-world test of attribution accuracy, signal recovery, and scalable tracking performance
Download Case StudyThe limitations of traditional tracking
Client-side tracking has long been the foundation of web analytics and digital marketing measurement. However, in today’s privacy-first environment, it’s showing its age. Browsers like Safari and Firefox now limit tracking capabilities through Intelligent Tracking Prevention (ITP) and Enhanced Tracking Protection (ETP). Add in growing ad blocker usage and increased consumer awareness, and you’re left with a fractured view of the customer journey.
For data-driven businesses, even a small drop in measurement accuracy can skew attribution models, misguide budget allocation, and break automated ad optimization. To better understand what’s being lost—and how to fix it—we put server-side Google Tag Manager (ssGTM) to the test.
What is server-side Google Tag Manager (ssGTM)?
Server-side GTM moves tag execution from the user’s browser to a secure cloud-based server environment. Instead of loading and firing tracking scripts on the client side — where they’re vulnerable to blocking and deletion — ssGTM executes these processes securely on the server side. This brings several distinct benefits:
• Greater control over cookies and unique identifiers
• Improved security and loading performance
• Increased resistance to ad blockers and browser restrictions
• Cleaner, more consistent tracking data for all platforms
Methodology: Controlled A/B experiment
Over a four-and-a-half-month period, we conducted a parallel-tracked A/B test comparing traditional client-side GTM (Container A) with server-side GTM hosted via Stape.io (Container B). Both containers were deployed simultaneously on the same live website and observed identical audience behaviour. This parallel tracking approach enabled a direct, apples-to-apples comparison of how each implementation handled data collection, attribution accuracy, and event integrity.
To enhance the performance of the server-side configuration, we leveraged two key features available through Stape:
- Custom GTM Loader: This enabled all tags to be served from our own domain, helping to bypass ad blockers that typically suppress third-party scripts.
- Cookie Keeper: This tool maintained and restored persistent user identifiers, even after deletion, improving session continuity, return visit tracking, and remarketing accuracy.
Together, these tools ensured our ssGTM container operated with greater stability, accuracy, and resilience across all browsers.
| Variant | GTM Container | GA4 Property | Tracking Type |
|---|---|---|---|
| A (Control) | Container A | GA4 A | Traditional Client-Side |
| B (Test) | Container B | GA4 B | Server-Side via Stape.io |
Results: Improved measurement across key metrics
The A/B test revealed clear and consistent performance gains when using server-side GTM across all major tracking categories. As visualized in the accompanying chart, the server-side container outperformed the client-side setup across all major tracking categories.
Google Ads Conversions (+24.18%)
Server-side GTM captured nearly one in four more conversions compared to client-side tracking—a substantial uplift with significant implications for paid media performance. This gain suggests that a large number of conversion actions were previously either lost or misattributed under the traditional setup.
For advertisers using smart bidding in Google Ads, missing data can result in suboptimal algorithmic decisions. Accurate conversion tracking is essential to inform bidding, budget allocation, and campaign scaling, making ssGTM not just a tracking upgrade, but a performance multiplier.
New Users (+4.02%)
Modern browsers and ad blockers increasingly suppress third-party cookies and scripts, making it harder to identify first-time visitors. The ssGTM helped restore visibility into new user sessions, improving the accuracy of acquisition reporting. With a 4% increase in new users, it enhanced audience segmentation, customer journey mapping, and top-of-funnel campaign analysis.
Total Users (+2.29%)
Even minor discrepancies in user counts can skew critical KPIs like cost-per-acquisition and conversion rate. The ssGTM setup resulted in a 2.29% increase in total user tracking, capturing both new and returning visitors who would have otherwise been missed. At scale, this translates to thousands of additional sessions, providing teams with a more comprehensive understanding of their site traffic.
Event Count (+2.92%)
Server-side GTM logged nearly 3% more total events than its client-side counterpart, reflecting more consistent and reliable tag execution. JavaScript-based events (clicks, scrolls, or interactions) are often blocked or suppressed at the browser level. This uplift enhances funnel tracking, behavioural analytics, and event-driven automation by ensuring that critical touchpoints are accurately recorded.
Key Events (+1.13%)
Key business events like form submissions, transactions, or demo requests are often the most valuable data points for performance reporting and lead generation. Even a 1–2% increase in these high-intent actions can make a meaningful impact on cost-per-lead and return on ad spend. Server-side GTM ensures that these signals are captured consistently, enabling better optimization and reporting precision.
Stape recovery overview: Recovered requests breakdown
* Number of recovered requests from ad blockers and browsers with tracking preventions over the selected period of time.
To supplement our A/B test findings, we reviewed data provided by Stape’s built-in analytics to further validate the impact of server-side tracking.
Over a 90-day period, our server-side GTM container processed more than 200,000 tracking requests. According to Stape’s system-level reporting, over 12% of these requests were successfully recovered from browser-level tracking disruptions — events that would have otherwise been lost in a traditional client-side setup.
- 3.37% of requests were blocked by ad blockers
- 8.62% were impacted by tracking prevention mechanisms (like ITP and ETP)
This means over 24,000 user interactions—including form completions, clicks, and pageviews—would have been lost entirely using a client-side implementation. The consistent rate of signal suppression and recovery across time, as illustrated in the chart, shows that server-side GTM restores a significant volume of business-critical data every single day.
Browser-specific recovery results
Looking at browser-specific results, even in Chrome — a browser without built-in tracking prevention — saw nearly 4% of requests recovered from ad blockers. More privacy-restrictive browsers like Safari also benefited, showing that ssGTM provides robust cross-browser data resilience.
Event-level breakdown: GA4 requests
*The breakdown of total requests and the percentage of requests impacted by ad blockers and tracking preventions (TP), categorized by event type, that were claimed by GA4 Client in server Google Tag Manager.
The most notable finding is that ScriptLoad events—essential for any tag to function—faced up to 17.55% interference across both blockers and browser-level prevention. Similarly, PageViews, a foundational metric in any analytics strategy, were interfered with in more than 14% of cases. Without server-side GTM, these data gaps would undermine campaign reporting, conversion tracking, and bid optimization.
Technical resilience: Other requests beyond GA4
* The breakdown of total requests and the percentage of requests impacted by ad blockers and tracking preventions (TP), categorized by event type, that were claimed by clients other than GA4 and Data Client. These other clients may include, but are not limited to: Cookie Keeper, JS events, GTM script loads, etc.
In addition to standard GA4 events, Stape’s analytics categorize a group of tracking activities as “Other Requests.” These refer to non-GA4 scripts and tag executions that are essential to broader marketing operations and web performance—but often overlooked when assessing tracking completeness.
Examples of what falls under “Other Requests” include:
- CustomScriptLoad events: These are custom scripts loaded through GTM or hardcoded into the site, often responsible for:
- Marketing automation scripts (e.g., HubSpot, Pardot)
- A/B testing and CRO tools (e.g., Google Optimize, VWO)
- Heatmapping tools (e.g., Hotjar, Crazy Egg)
- Third-party lead form logic
- Affiliate or partner tracking pixels
- Marketing automation scripts (e.g., HubSpot, Pardot)
- CookieKeeper scripts: This includes logic injected to extend or restore first-party cookies (e.g., for maintaining user session continuity across ITP environments).
- Consent Manager integrations: These scripts are used to load or trigger cookie banners, privacy toggles, and other components essential for legal compliance with GDPR/CCPA.
- JS utility tags: GTM or manually added JavaScript tags that perform lightweight but essential tracking logic—such as click listeners, time-on-page triggers, or scroll-depth events.
- Internal event triggers: These include server-side requests used to manage tag sequencing, cross-domain tracking, or conditional fire rules that don’t fall under the GA4 schema but are important for orchestrating analytics and marketing tags.
These suppression rates (close to or above 8%) mean that 1 in every 12 utility or custom scripts failed to execute on a client-side setup due to browser protections. These failures don’t just lead to lost data; they can cause entire toolsets (like form tracking, CRO tests, or cookie compliance systems) to break or go undetected.
Server-side GTM ensures these tools operate in a protected environment, unaffected by the increasingly hostile landscape of browser-level privacy controls and ad-blocking extensions.
Scaling the benefits: Why ssGTM matters more with traffic rowth
The results of our case study clearly demonstrate that server-side GTM delivers more accurate, complete, and resilient data—across user tracking, event logging, and conversion attribution. While the percentage improvements we observed may seem modest in isolation, their impact compounds dramatically as traffic increases.
For businesses operating at scale, even a small drop in data accuracy can result in:
- Skewed performance insights
- Inefficient media spend
- Suboptimal automated bidding
- Missed customer opportunities
Here’s why that matters:
1. Undercounting Users Skews Cost Metrics
A 2–4% underreporting of total or new users can artificially inflate your cost-per-acquisition (CPA) and cost-per-click (CPC) metrics. Marketing teams may mistakenly assume a campaign is underperforming and reduce spend on initiatives that are actually working.
2. Undercounted Conversions Lead to Under-Optimized Campaigns
In our case study, server-side GTM captured 24.18% more Google Ads conversions compared to client-side tracking. This isn’t just a reporting gap—it’s a strategic handicap.
When Google Ads doesn’t receive complete or timely conversion data, its algorithm lacks the fuel it needs to:
- Learn which users are most valuable
- Optimize bidding strategies
- Identify high-performing keywords or creatives
- Scale campaigns effectively
Incomplete data can lead to misleading performance signals within smart bidding strategies (like Target CPA or Maximize Conversions), which may result in marketers making suboptimal decisions—such as reducing budgets or deprioritizing campaigns that are actually performing well.
3. Missed Events Compromise Automation and Personalization
Missing even a few key engagement events—like form submissions, product views, or cart additions—each day can result in:
- Broken retargeting audiences
- Inaccurate funnel drop-off reporting
- Incomplete CRM handoffs
- Lower automation trigger accuracy (e.g., nurture emails, ad sequences)
Over weeks and months, these missed signals add up to hundreds or thousands of lost data points, which can degrade the effectiveness of full-funnel marketing efforts.
4. Scaling Amplifies the Impact
At smaller traffic volumes, the cost of lost signals may be hard to detect. But as you scale:
| Monthly Sessions | 2.5% Missed Events | 24% Missed Conversions |
|---|---|---|
| 10,000 | 250 lost events | 240+ unreported conversions |
| 100,000 | 2,500 lost events | 2,400+ missed conversions |
| 500,000 | 12,500 lost events | 12,000+ missed conversions |
For high-growth or enterprise businesses, these discrepancies can mean millions in missed revenue attribution—and poorly informed strategy decisions.
“Implementing server-side GTM has fundamentally changed how we think about marketing data. The ability to recover lost signals and attribute conversions more accurately has been a game changer for both our team and our clients. It’s not just about better tracking—it’s about making smarter, more confident decisions.”
— Brock Murray, Co-Founder & COO, seoplus+
This case study demonstrates that server-side Google Tag Manager (ssGTM) is not just a technical improvement—it’s a foundational shift in how businesses can track, attribute, and optimize performance in today’s privacy-constrained digital environment.
Conclusion
Over the course of our four-and-a-half-month A/B test, ssGTM consistently outperformed traditional client-side tagging across all major metrics. Most notably, it captured 24.18% more Google Ads conversions, recovered up to 12% of signals lost to browser restrictions and ad blockers, and delivered cleaner, more consistent event data. These uplifts weren’t theoretical—they translated into tangible improvements in attribution accuracy, campaign visibility, and marketing decision-making.
With added resilience from tools like Stape’s Custom Loader and Cookie Keeper, the server-side configuration provided enhanced control over tracking infrastructure while remaining agile, scalable, and compliant with evolving privacy standards.
As businesses grow and digital campaigns become increasingly automated and data-dependent, the cost of incomplete tracking rises exponentially. Server-side GTM ensures that critical data isn’t lost at the browser level—and that ad platforms, analytics tools, and automation systems are fueled by accurate, comprehensive information.
In short: ssGTM strengthens the integrity of your entire marketing stack. For any organization serious about performance measurement, privacy resilience, and long-term scalability, server-side tracking isn’t just an upgrade—it’s a strategic imperative.
Interested in implementing server-side GTM?
Get in touch with the team at seoplus+ to explore how server-side tagging can help your business unlock cleaner data, stronger attribution, and smarter performance insights.
