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Impact of on Website Speed
Impact of on Website Speed
Joe Scanlon avatar
Written by Joe Scanlon
Updated this week

Some teams would like to understand the impact of on their websites. This guide explores website performance through a series of tests in a controlled environment. The results confirm that is an efficient tool with minimal impact on site performance.

Additionally, you may minimize the impact of by restricting its access to only invited users and, if desired, disabling the Session Replay feature.


A structured test was conducted using a basic HTML page to isolate the performance impact of

  • Without Establishing a performance baseline.

  • With (Session Replay Disabled): Analyzing the impact of the core functionality.

  • With (Session Replay Enabled): Assessing the full feature set, including session replay.

Google Page Speed Insights was utilized to measure key performance indicators.

Explanation of Google Page Speed Insights Metrics

Google Page Speed Insights is a tool that analyzes the performance of a webpage and provides insights on various metrics that affect user experience. Here's a breakdown of the key performance indicators it measures:

  1. First Contentful Paint (FCP):

    • What it is: The time it takes for the first piece of content to be rendered on the screen.

    • Why it matters: A fast FCP helps assure users that something is happening and the page is loading, reducing the likelihood of them leaving the site.

  2. Largest Contentful Paint (LCP):

    • What it is: The time it takes for the largest piece of content (such as an image or a large text block) to be fully rendered.

    • Why it matters: LCP is critical for understanding when the main content of the page is visible to users. A fast LCP indicates that the page is useful quickly.

  3. Total Blocking Time (TBT):

    • What it is: The total amount of time that a page is blocked from responding to user input (like clicks or key presses) due to long tasks.

    • Why it matters: Lower TBT ensures that the page is interactive and users can engage with it without experiencing delays.

  4. Cumulative Layout Shift (CLS):

    • What it is: A measure of how much the layout of the page shifts during its loading phase.

    • Why it matters: A low CLS means the page elements don't shift around unexpectedly, providing a stable and predictable layout which is crucial for good user experience.

  5. Speed Index (SI):

    • What it is: A measure of how quickly the content is visually displayed during page load.

    • Why it matters: The Speed Index gives an overall impression of the loading speed from the user's perspective. Lower scores mean faster visual loading.

Test Results


Baseline Performance (Replay Disabled) (Replay Enabled)

Performance Score




First Contentful Paint (FCP)

0.2 s

0.4 s

0.2 s

Largest Contentful Paint (LCP)

0.2 s

0.4 s

0.2 s

Total Blocking Time (TBT)

0 ms

10 ms

140 ms

Cumulative Layout Shift (CLS)




Speed Index (SI)

0.2 s

0.6 s

0.4 s

Analysis has proven to be exceptionally lightweight, with minimal impact on primary loading metrics such as FCP and LCP, even when fully featured with session replay. The slight variations in TBT and SI when session replay is activated are modest and do not compromise the overall user experience. These results underscore the efficiency of, particularly in maintaining fast load times and a stable layout, crucial for user satisfaction and SEO performance.


Integrating, including its session replay capabilities, is highly effective and has a negligible effect on website performance in a simple testing environment. With its minimal impact on crucial performance metrics and the significant value it adds in terms of user engagement and feedback capabilities, is an excellent tool for enhancing your website’s functionality.


  • Adopt Given its minimal performance footprint and substantial benefits in user interaction and debugging, is recommended for enhancing your website’s functionality.

  • Performance Monitoring: Continue to monitor website performance metrics regularly to ensure that all functionalities are optimized.

  • Optimization Techniques: Implement best practices such as asynchronous loading or deferring non-critical scripts to further enhance site performance.

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