---
title: Impact of Fibr Script on Web Performance
slug: impact-of-fibr-script-on-web-performance
docTags: 
createdAt: 2026-09-01T09:47:30.938Z
---

Every script you add to your website affects performance. We know that slower pages mean lower conversions, so we've engineered the Fibr Script to be as lightweight as possible.

To show you exactly what that means, we ran a head-to-head comparison of Fibr against other popular personalization tools: VWO, Kameleoon, and Mutiny. Here's what we found.

## Performance Comparison

We measured four key metrics that directly affect user experience and Core Web Vitals scores. Lower impact percentages are better.

### Overall Performance Score

| **Tool**  | **Without Script** | **With Script** | **Impact** |
| --------- | ------------------ | --------------- | ---------- |
| **Fibr**  | 68.6               | 61.9            | **-9.77%** |
| VWO       | 68.6               | 58.0            | -15.45%    |
| Kameleoon | 68.6               | 57.2            | -16.62%    |
| Mutiny    | 68.6               | 58.5            | -14.72%    |

**Fibr's impact is 35-40% lower than competitors.**

***

### First Contentful Paint (FCP)

FCP measures how quickly the first visible content appears. Faster is better for perceived load speed.

| **Tool**  | **Without Script** | **With Script** | **Impact** |
| --------- | ------------------ | --------------- | ---------- |
| **Fibr**  | 0.91s              | 0.99s           | **+8.79%** |
| VWO       | 0.91s              | 1.15s           | +26.37%    |
| Kameleoon | 0.91s              | 1.11s           | +21.98%    |
| Mutiny    | 0.91s              | 1.14s           | +25.27%    |

**Fibr adds less than 0.1 seconds. Competitors add 0.2 seconds or more.**

***

### Largest Contentful Paint (LCP)

LCP measures when the largest visible element finishes loading. This is a Core Web Vital that affects your SEO.

| **Tool**  | **Without Script** | **With Script** | **Impact**  |
| --------- | ------------------ | --------------- | ----------- |
| **Fibr**  | 1.92s              | 2.21s           | **+15.10%** |
| VWO       | 1.92s              | 2.31s           | +20.31%     |
| Kameleoon | 1.92s              | 2.15s           | +11.98%     |
| Mutiny    | 1.92s              | 2.60s           | +35.42%     |

**Fibr stays competitive on LCP, with Kameleoon slightly ahead on this specific metric.**

***

### Total Blocking Time (TBT)

TBT measures how long the main thread is blocked, preventing user interaction. Lower is better for responsiveness.

| **Tool**  | **Without Script** | **With Script** | **Impact**  |
| --------- | ------------------ | --------------- | ----------- |
| **Fibr**  | 481ms              | 587ms           | **+22.04%** |
| VWO       | 481ms              | 726ms           | +50.94%     |
| Kameleoon | 481ms              | 953ms           | +98.13%     |
| Mutiny    | 481ms              | 575ms           | +19.54%     |

**Fibr and Mutiny are close here, while Kameleoon nearly doubles blocking time.**

***

## The Bottom Line

No personalization script has zero impact, but Fibr consistently ranks in the top two across all performance metrics. In most cases, the difference is significant: competitors often add 2-3x more overhead than Fibr.

We're continuing to optimize. Our goal is to make the performance impact negligible so you can personalize confidently without sacrificing speed.

***

## Tips to Maximize Performance

Even with Fibr's lightweight script, you can further minimize impact:

- **Place the script at the top of your \<head> tag.** This ensures it loads early and doesn't compete with other resources.
- **Avoid installing via Google Tag Manager.** GTM adds latency that can increase FCP and cause flickering. Direct installation is faster.
- **Use the anti-flicker snippet if needed.** Available in your Setup dashboard, this prevents the flash of original content before personalization loads.
- **Keep your \<head> clean.** The fewer scripts competing for the main thread, the better your overall performance.