The 5 Most Underrated WebPageTest Features

WebPageTest is one of the best website speed auditing services for any designer or developer concerned with site speed (which should be all of them). We use it as the engine for our automated testing services at However, we often see WebPageTest utilized only in its simplest form, which is a little like driving a Lamborghini to the store down the street. Sure, it does the job just fine, but let’s get this thing out onto the open road!

There is actually an entire suite of advanced features that give you an unparalleled view of your site from a performance standpoint. WebPageTest has good documentation, but it isn’t the most beginner-friendly. This makes many afraid to try some of their more advanced features.

Fear not. We’ve combed through that documentation to bring you a simple guide of what are, in our humble opinion, the 5 most underrated WebPageTest features that you should be using on your site.

Visual Comparison

Who are your competitors in your website’s niche?

If you’re running a successful e-commerce site, you likely have a large number of competitors, as you’re all fighting for the same potential customers.

Even if you run a small blog, your site still has competition. There is a finite number of people who are interested in the content you’re creating, and you want to capture as much of that market as possible. We won’t get too deep into search engine optimization, but speed optimization is a huge part of what sets your site apart from others.

WebPageTest allows you to compare your site directly to a competitors with their Visual Comparison tool!

WebPageTest Visual Comparison Tool

By simply inserting 2 (or more) URLs into this tab, we can compare their load times and see a filmstrip of the results.


Looks like Amazon has their Largest Contentful Paint occur around a half-second faster than Target. Thankfully we recently created a list of improvements Target can make to close the gap!

Similarly, you can use this tool to see how you compare to others in your content area and find where you can make up ground.

Capture Lighthouse Report

This feature is more of an ‘everything in one place’ feature. Google’s Web Vitals are a key group of metrics in web performance, so it makes sense to see where you rank using Google’s Lighthouse as well.

Capture Lighthouse report

By selecting ‘Capture Lighthouse Report’, you’ll see that score added to the results at the top of your audit.

Lighthouse perf results

Keep in mind that this test is run using a “3G Fast” connection, so it will likely look pretty slow. However, it is equally important to test how your website performs on slower devices and internet connections, so this information is incredibly useful.

WebPageTest Scripting

Need to speed test a website that lives behind a login? Want to see how performant your e-commerce check-out process is? Scripting with WebPageTest will be invaluable for you.

In short, this powerful tool allows you to test a multiple-step process through different parts of your site.

You may test a product page on your site and see great results, but your customers experience a terribly slow checkout process and don’t complete the sale out of frustration. This is a weak link in the system that has to be found for your business to be successful.

This feature is actually our absolute favorite, so we have an entire article dedicated to it here! You’ll see how to build and run your script, as well as all of the benefits.

Block Requests

If you run ads, tracking pixels, chat snippets, etc. on your site, you’ll likely want to test your site to see how much performance you’re giving up.

With the Block Requests feature, you can do just that. Simply enter the domains or URL substrings you’d like to block, and run the test. This will be your baseline. After this test is complete, run a test on your site without blocking, which will show how much additional time is added.

Andy Davies wrote an excellent piece that details how to compare the 2 tests and view a filmstrip showing the performance cost of 3rd party resources.

Single Point of Failure (SPOF) Test

According to HTTPArchive, websites load an average of 21 third-party assets. These range from Google Fonts, analytics, and tracking, to ad servers, to social media widgets, and beyond.

But what happens when one of these external resources times out?

Does your website keep on humming without skipping a beat, or does the entire site render as a blank page while the server waits for a response that never comes? If the failing script or stylesheet has a blocking function, everything that gets loaded after it has to wait. As does your visitor!

With the WPT SPOF test, you can see what happens when a third party script time out. If you determine that a certain asset would completely break your site, then it’s important to find a solution. Asynchronous integrations ensure that nothing is waiting on a specific script or stylesheet. You can also host a local file on your site to be loaded in case your CDN of choice goes down.

This test is also a good way to choose between different providers of a script or service. If one offers an asynchronous set up that wouldn’t create a single point of failure, and the other one does not, the chouse is clear!

WebPageTest Underrated Features Put You Ahead of the Curve

Some of the features we list above may seem like overkill. But ask yourself this.

How many of my competitors are using these tools?

The answer is probably very few. If you are, then you are easily a few steps ahead of them.

Too many website owners, designers, and developers insert third party functionality with no regard for how it might impact performance. Using Scripting and Blocking alone can help you decide between different vendors and help you choose the one that’s most performant.

Make sure to use the Visual Comparison Test as well, and see how you stack up with your competition. Get your site to display faster than theirs, and reap the rewards!

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