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Impact of Fibr Script using GTM

See how the Fibr Script performs across key metrics like FCP, LCP, and Total Blocking Time if placed using Google Tag Manager.

You can install the Fibr Script through Google Tag Manager, but we recommend against it. Here's why.

The Problem with GTM Installation

Google Tag Manager adds an extra layer between your page and the Fibr Script. This delay affects how quickly Fibr can initialize and deliver personalized experiences.

The result? Slower performance metrics and a higher chance of flickering, where visitors briefly see your original page before the personalized version loads.

Performance Comparison: Direct vs. GTM

We tested the same Fibr Script installed two ways: directly in the <head> tag versus through Google Tag Manager.

Metric
Direct Installation
Via GTM
Performance Hit

First Contentful Paint (FCP)

0.99s

1.15s

+160ms (+16%)

Largest Contentful Paint (LCP)

2.21s

2.31s

+100ms (+5%)

Total Blocking Time (TBT)

587ms

726ms

+139ms (+24%)

GTM adds roughly 100-160ms of delay across key metrics. That might not sound like much, but it's enough to cause visible flickering and can hurt your Core Web Vitals scores.

When GTM Might Be Acceptable

Direct installation is always the better choice, but we understand that some teams have constraints. GTM installation may be acceptable if:

  • You don't have direct access to your site's HTML

  • Your organization requires all scripts to go through GTM for governance reasons

  • The pages you're personalizing aren't performance-critical (e.g., internal tools, low-traffic landing pages)

If you do use GTM, test thoroughly for flickering and monitor your Core Web Vitals after deployment.

Our Recommendation

Install the Fibr Script directly in your <head> tag whenever possible.

Place it at the very top, before analytics tags and other third-party scripts. This gives Fibr the best chance to load early and deliver experiences without delay.

Need help with direct installation? See our setup guides:

If you're stuck with GTM and experiencing issues, reach out to us at support@fibr.ai. We can help you optimize your setup.

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