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How to Test Website Performance - Best Website Optimization Tools

Author profile imageLars Salling·May 28, 2023
A close-up photo of a person using a laptop computer.

Whether you are in charge of a simple blog or a larger corporate site, testing and auditing your website’s performance is an important routine that can help catch unnecessary load times and other unwanted issues on your site.

This article will be mostly focused on how to test website performance in terms of load speed, though it is also common to test for other things such as accessibility and website functionality (which may often be done through more technical integration tests).

What does a website testing tool do?

A website speed testing tool is a tool that performs performance audits on web pages, often through a specified URL to the page that is tested. When a testing tool is given a URL, it will in most cases send a web request to the url and inspect it as if it was a human interacting with the site, and after the audit it’ll be able to provide some important metrics about the web page. Some of the most common things that are tested are:

  • Load time: how long it takes to access the website through the network
  • Time to interactive (TTI): how long it takes before a user is able to interact with the website
  • External requests: how many requests a website makes after being loaded (fx. loading more image and video files)

What are the best website speed test tools?

Many speed website speed test tools are free and available on the internet, and while most of them work in the same way by providing a URL to the web page that you want tested, they may have different ways of measuring the speed of your website.

The most popular website speed testing tools are:

Google PageSpeed Insights

PageSpeed Insights is a website that allows you to audit your website’s performance among other important factors such as accessibility and SEO.

One of the main benefits of PageSpeed Insights is that it’s developed by Google and will give you reliable and important metrics on your website that indicates how well it performs both for visitors and search engines (if you are interested in ranking). A subset of these metrics are called Web Vitals and include scores such as:

  • First Contentful Paint (LCP): how long it takes before a website’s main content has been loaded fully.
  • Total Blocking Time (TBT): how much time passes before a web page is usable by the visitor
  • Cumulative Layout Shift (CLS): how much a website shifts during page loading (eg. when advertisements are loaded a bit delayed from the rest of the content, making the website jump a little)

In PageSpeed Insights, these metrics (among others) are displayed on a score of 1 to 100, making it easy to debug and improve the different metrics when optimizing your website.

Screenshot of PageSpeed Insights' performance tab

If you wish to read more about the different metrics produced by PageSpeed Insights, you can see an overview of the different metrics here.

Pingdom Website Speed Test

Another great speed testing tool is the Website Speed Test by Pingdom, which, just like PageSpeed Insights, lets you input a URL to a webpage and then the tool will analyze and audit the performance of that page.

The Pingdom Website Speed Test outputs an overall performance grade among other important factors such as total page size, load time and the amount of requests made after the web page was loaded. A very useful feature of the tool is the “Content size by content type” overview that shows how much of your website’s size is taken by each content type.

A screenshot of Pingdom's audit tool showing the size of different content types on a website load.

This is especially useful when making sure that you’re not downloading redundant or unoptimized content.

GTmetrix Website Performance Testing

A more thorough tool for doing performance testing of your website is the GTmetrix Website Performance tool, which works the same as the previous two by inputting a URL. The benefit of GTmetrix is that it provides a more detailed and thorough analysis of the page that you are testing, which can be very beneficial if you want to do more fine-grained optimizations to your webpage.

A screenshot of GTmetrix' waterfall chart showing when different files are loaded on a website.

While GTmetrix has common metrics like LCP, TBT and CLS (like PageSpeed Insights), it also has a tab for analyzing the request waterfall of a website load in order to see which files are loaded when. This can be very helpful when debugging long loading times.

What to do from here

Now that you’ve learned how to test your website’s performance and which tools you can use for that, you need to start optimizing. While most of the tools that we’ve mentioned in this article will have some guides to optimize your website, we advise that you read our article on how to make a website load faster, which includes a bunch of tips and tricks you can do in order to optimize your website.

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Frequently asked questions

How to test a website on different browsers

Common website testing tools like PageSpeed Insights or Pingdom use the Chrome browser as the testing agent, though some tools allow you to select which browser/agent you want to perform the test through.