---
updatedAt: 2026-04-11T02:12:14.000Z
agentTools:
  projectIndex: https://docs.developers.convert.com/v1.0-web/llms.txt
---

# Performance Trade-Offs

## Overview

Convert's tracking script presents a fundamental choice between **user experience consistency** (no flicker) and **Core Web Vitals optimization** (better page speed scores).

## Script Metrics

| Metric           | Value                              |
| ---------------- | ---------------------------------- |
| Base script size | \~50 kB (compressed, over network) |
| Page load impact | \~100ms additional                 |
| Processing time  | \~200ms for experience application |

Script size increases with the number of active experiences, locations, audiences, and goals in the project.

## Core Web Vitals Impact

### Largest Contentful Paint (LCP)

* **Synchronous:** Moderate to high impact (script is render-blocking)
* **Asynchronous:** Minimal impact

### First Input Delay (FID)

* **Synchronous:** Moderate impact (\~200ms processing)
* **Asynchronous:** Minimal impact

### Cumulative Layout Shift (CLS)

* **Both modes:** Low to moderate (depends on experiment design)
* **Mitigation:** Use anti-flicker techniques and reserve content space for elements that change

## When to Choose Synchronous Loading

* User experience consistency is critical
* A/B testing accuracy is paramount
* Flicker effects are unacceptable
* Core Web Vitals are not a primary SEO concern

```html
<script src="//cdn-4.convertexperiments.com/v1/js/[account_id]-[project_id].js"></script>
```

## When to Choose Asynchronous Loading

* Core Web Vitals optimization is critical for SEO
* Page speed is prioritized over perfect UX consistency
* Slight flicker is acceptable for better performance

See the [Anti-Flicker Async Loading](/recipes/anti-flicker-async-loading) recipe for the complete async snippet with built-in flicker protection.