24% more Google Ads conversions from a 4.5-month A/B test: server-side GTM vs client-side | seoplus+

seoplus+ is a digital marketing agency specializing in performance-driven marketing, analytics, and optimization. With a strong focus on data accuracy and privacy-compliant tracking, the team constantly tests new methods to improve marketing measurement and attribution. In this experiment, seoplus+ tested advanced tracking solutions on their own website to directly understand the impact of server-side Google Tag Manager (sGTM) in a real-world environment.

Traditional client-side tracking has become increasingly unreliable. Browsers like Safari and Firefox limit tracking via Intelligent Tracking Prevention (ITP) and Enhanced Tracking Protection (ETP), while growing ad blocker usage and consumer privacy awareness further disrupt data collection. For data-driven businesses, these gaps in tracking can:

• Skew attribution models
• Misguide budget allocation
• Impair automated ad optimization

In practice, even minor losses in measurement accuracy meant missed conversions, incomplete funnel visibility, and under-optimized campaigns. Until now, seoplus+ had relied entirely on web tracking, but these challenges prompted them to explore server-side GTM for the first time to overcome these limitations.

To address the limitations of fragmented client-side tracking, seoplus+ implemented server-side tracking via Stape, moving tag execution from the user’s browser to a secure server environment. Unlike client-side GTM, which runs scripts in the browser and is often blocked by ad blockers or browser restrictions, sGTM executes tags on a server, improving data accuracy, extending cookie lifespan, and ensuring more reliable tracking.

A four-and-a-half-month A/B experiment was conducted on the seoplus+ website, using two GA4 containers:

• Container A with traditional client-side GTM as the control.

• Container B with server-side GTM hosted via Stape as the test.

Both containers tracked the same real user traffic, capturing pageviews, clicks, form submissions, and conversions.

To further reduce signal loss and improve measurement, Stape’s Custom Loader was activated to serve tags from the seoplus+ domain, bypassing blockers, and Cookie Keeper maintained persistent user identifiers for session continuity and accurate remarketing. 

On top of this setup, Stape Analytics was used to validate the results. Available inside every Stape account, this feature visualizes how many requests are blocked or stripped client-side and how many are recovered server-side. By reviewing Stape Analytics throughout the test, seoplus+ could clearly see where browser restrictions interfered with data and how much information was being restored with server-side GTM.

Over the course of the experiment, 200,000+ real user requests were analyzed, allowing for a direct comparison of tracking accuracy, event capture, and conversion measurement between client-side and server-side setups.

The server-side GTM implementation on the seoplus+ website delivered clear improvements across all major metrics:

Server-side GTM recovered 12% of interactions lost to ad blockers and browser tracking prevention, including clicks, pageviews, and form submissions. Even browsers with stricter privacy rules, such as Safari and Firefox, saw significant recovery.

Critical events and scripts – like pageviews, form submissions, marketing automation, and A/B testing tools – were captured reliably, ensuring accurate analytics, attribution, and automation.

At scale, these improvements translate into thousands of recovered events and conversions, directly enhancing marketing measurement, optimization, and decision-making.

Stape Analytics doesn’t just report totals – it categorizes data by client (e.g., GA4, Data Client) and by event type, so marketers can see exactly where browser restrictions or ad blockers interfered, and how many signals were successfully restored server-side. This makes it possible to prove improvements in data quality, justify ad spend, and optimize campaigns with confidence.

Using Stape Analytics, seoplus+ measured over 90 days that their server-side container processed 200,000+ requests:

• 12% recovered from browser-level disruptions
• 3.37% blocked by ad blockers
• 8.62% impacted by ITP/ETP

Over 24,000 interactions – form completions, clicks, and pageviews – would have been lost with client-side tracking. The list above shows that sGTM consistently restores this business-critical data every day.

Chrome recovered ~4% of requests from ad blockers, while stricter browsers like Safari saw higher gains – showing sGTM strengthens tracking across all browsers.

GA4 data showed heavy interference: ScriptLoad events faced 17.55% disruption and PageViews over 14%. Without sGTM, these gaps would weaken reporting, conversions, and bid optimization.

Stape Analytics groups non-GA4 scripts and tag executions under “Other Requests” – critical but often-overlooked tracking activities. These include marketing automation (HubSpot, Pardot), CRO/heatmapping tools (VWO, Hotjar), affiliate pixels, Cookie Keeper, consent managers, utility JS tags, and internal server-side triggers.

On client-side setups, 8%+ of these requests were blocked, meaning 1 in 12 essential scripts failed, breaking form tracking, CRO tests, or compliance tools. With server-side GTM, these scripts run reliably in a protected environment, unaffected by browser privacy controls or ad blockers. As more businesses look to maximize their marketing ROI, understanding how server-side testing improve conversion rate optimization outcomes becomes a crucial step in maintaining accurate attribution and reducing lost events. 

Even small losses scale into thousands of missed conversions and events, directly affecting ROI, automation, and attribution.

Client-side tracking was losing conversions and critical event data due to browser restrictions and ad blockers. By implementing server-side GTM via Stape, seoplus+ ensured tags and identifiers ran reliably, with Stape Analytics validating recovery and improvements. The result: 24% more Google Ads conversions, 12% of previously lost interactions recovered, and consistent tracking across all browsers, providing cleaner data for better attribution, ROI, and marketing decisions.

• Server-side GTM recovers lost conversions and events blocked by browsers or ad blockers.
• Critical scripts, marketing automation, and analytics tools run reliably.
• Stape Analytics clearly visualizes recovery and performance improvements.
• At scale, recovered interactions translate to thousands of events and conversions.

• Quick, practical setup without heavy development.
• Custom Loader and Cookie Keeper ensure reliable tag execution.
• Built-in Analytics offers transparency on tracking recovery.
• Protects data across browsers, improving attribution, campaign optimization, and ROI.