Google Lighthouse Performance

The Google Lighthouse performance score is a metric that measures the speed and performance of a website. It’s an overall score that ranges from 0 to 100 and is generated based on a number of different performance metrics, such as the time it takes for a website to load, the time it takes for a website to become interactive, the size of the resources used by the website, and other factors that impact the user experience.

A high performance score in Google Lighthouse indicates that a website is fast and responsive, which can lead to a better user experience and improved search engine rankings. On the other hand, a low performance score can indicate that a website is slow and unresponsive, and can negatively impact the user experience.

Mobile Performance
Desktop Performance

Core Web Vitals

Core Web Vitals are a set of specific factors that Google considers important in a webpage’s overall user experience. Core Web Vitals are made up of three specific page speed and user interaction measurements: Largest Contentful PaintFirst Input Delay, and Cumulative Layout Shift.

Largest Contentful Paint3.9 s1.0 s< 2.5 s
First Input Delay220 ms30 ms< 100ms
Cumulative Layout Shift0.9160.738 0.1

Tracking scripts

All the tracking scripts on the site generated ~40 KB of data

A tracking script is a code snippet designed to track the flow of visitors who visit a website. Media, advertising, and analytics organisations will provide a script to add to your website that sends data directly to their servers. This data can then be used to measure goals and conversions, analyse user behaviour, and influence advertising campaigns.

Consider how much of this data you actually need and use? How often do you review the analytics data, and does this inform genuine change? Are you actively running social media campaigns? Consider pausing or removing tracking scripts that aren’t being actively used. 1 40 KB


Optimise images

By optimising the following images, roughly 225 KB could be removed from the transfer size, about 24%. This would reduce the CO2 generated per page load from 0.21g grams to 0.16 grams.

Images should be optimised for the web for several reasons:

  1. Reduced file size: Optimizing images can result in a smaller file size, which can help to reduce the amount of data that needs to be downloaded. This can lead to faster page load times and improved performance.
  2. Improved user experience: Optimising images can help to improve the overall user experience, as pages with optimised images load faster and are more responsive.
  3. Lower emissions: Optimising images can help to reduce the emissions associated with data transfer, as less data needs to be transmitted over the network.
  4. Better accessibility: Optimising images can make them more accessible to users with slower connections or limited data plans.

First Contentful Paint

First Contentful Paint (FCP) is a performance metric that measures the time it takes for the first piece of content to be rendered on the screen when a user navigates to a web page. This content can be any visual element on the page, such as text, images, or a background color.

FCP is important because it directly affects the perceived speed of a website, and can impact user engagement and conversion rates. A faster FCP can lead to a better user experience and improved performance.

Here are a few ways you can optimise your FCP:

  1. Optimise images: Large, unoptimised images can slow down a page’s FCP. You can optimise images by compressing them, reducing their dimensions, and choosing the right format for each image.
  2. Minimise HTTP requests: Each resource requested by a web page, such as images, scripts, and stylesheets, requires a separate HTTP request. Minimising the number of HTTP requests can help to reduce the time it takes for a page to render.
  3. Prioritize critical content: Prioritizing critical content, such as above-the-fold content, can help to ensure that users see something on the screen quickly, even if the rest of the page is still loading.
  4. Reduce server response time: A slow server response time can significantly impact FCP. Optimizing server-side code and server settings can help to reduce response times and improve FCP.
  5. Use a performance monitoring tool: There are many tools available that can help you monitor your website’s performance, including FCP. These tools can help you identify performance issues and track your progress as you implement optimizations.
Timing1.2 s0.4 s

Largest Contentful Paint

Timing3.9 s1.0 s

Total Blocking Time

Timing510 ms0 ms

Cumulative Layout Shift


Speed Index

Timing6.6 s1.9 s

Time to Interactive

Timing7.5 s0.4 s

Max Potential First Input Delay

Timing220 ms30 ms

Eliminate render-blocking resources

InsightPotential savings of 170 ms

Properly size images

InsightPotential savings of 101 KiB

Reduce unused CSS

InsightPotential savings of 26 KiBPotential savings of 25 KiB

Reduce unused JavaScript

InsightPotential savings of 24 KiBPotential savings of 24 KiB

Serve images in next-gen formats

InsightPotential savings of 84 KiBPotential savings of 225 KiB

Reduce initial server response time

InsightRoot document took 620 msRoot document took 670 ms

Avoid serving legacy JavaScript to modern browsers

InsightPotential savings of 11 KiBPotential savings of 11 KiB

Avoid an excessive DOM size

Insight1,290 elements1,290 elements

JavaScript execution time

Timing0.7 s0.1 s

Minimize main-thread work

Timing12.8 s2.4 s

Largest Contentful Paint image was lazily loaded