How to measure web performance in 2023

For website owners, web performance is an important topic, as it directly impacts important business KPIs such as conversion rate, user engagement, and Google search ranking.

Before investing in driving traffic to your site, optimizing web performance is essential, as it will improve both traffic and conversion simultaneously.

To achieve and maintain good web performance, you have to know how to measure your page's performance. Unfortunately, people are often confused because there are so many metrics and tools to choose from. This article will show you how to measure web performance in 2023.

Measuring web performance

What do we try to measure?

At its core, web performance is about the user experience. When you visit a website, pay attention to three key factors:

• How fast is the page loading?
• Is this site useful?
• Is this site usable?

Over the last few years, the World Wide Web Consortium (W3C) and browser vendors have invented a lot of metrics, scores, and tools to measure page speed and usefulness as accurately as possible. As a result, we made significant progress, but there is still much to do.

What is field and lab data?

You can measure web performance in two ways:

• In the field: by collecting performance data from users visiting your site. Field data helps you understand if and where users struggle. To limit impact on user experience and privacy, the amount of data you collect should be limited.
• In the lab: lab data is collected via a tool that visits a single URL. Because you are not impacting users, you can collect as much data as possible. This rich data helps you understand the cause of the problem.

You will want to measure both field and lab data to get the complete picture. We recommend the following workflow to maintain good web performance:

• Do automated lab tests in your release process to ensure you don't introduce web performance problems.
• Release new features to a small user group first in order to get field data. Then, if there are no performance problems, you can roll out the new features to more and more users.
• Monitor your website continuously with a real user monitoring (RUM) tool to spot performance problems before they impact your search ranking.
• If you see problems in your field data, use lab tools to get more insights.
• Use lab tools to A/B test multiple solutions to find the most effective fix for your problem.

We often encounter teams relying on lab tools to spot problems. However, we do not recommend this. Lab tools emulate older devices and slower network conditions, and this means lab data is often worse than field data. Using these tools might mean you spend time and money fixing issues that do not negatively impact your users. Instead, working on new features might be more beneficial for your business.

What are the best metrics to use?

There are plenty of performance metrics to choose from. In the following section, we will look at the most relevant ones.

Page load time

This metric is still one of the best-supported metrics among all browsers and tools. It measures the time from the navigation start until all page assets are loaded.

The metric became less valuable when the web pages became more complex. Current metrics focus only on the visible part of the website. These metrics correlate much better with business KPIs.

The Lighthouse Score

The Lighthouse score considers multiple metrics and transforms them into a number between 0 (poor) and 100 (good).

I don’t recommend using the Lighthouse Score as a web performance goal for the following reasons:

• The Lighthouse Score uses some metrics that only can be measured in the lab. Therefore the Lighthouse Score is not representing the user experience of your visitors.
• A perfect Lighthouse Score does not guarantee a great user experience. 50% of the pages with a Lighthouse Score of 100 don't have a good Web Vitals score.
• The Lighthouse Score is too volatile. The Lighthouse team has been changing the metrics and weights. And depending on your tool, you can get different results for the same page. Different scores for the same page often lead to confusion and unnecessary escalations.
• Page speed, usefulness and usability matter to website visitors. A single score doesn't give you enough insight to understand when and how you should optimize your website according to these factors.
• Teams can make decisions that ultimately hurt the user experience just to achieve the maximum Lighthouse Score. The highest priority should always be the user experience and not the score.

I think Google should have retired the Lighthouse Score after introducing Web Vitals and only kept the audit, which helps developers identify optimization opportunities.

But the Lighthouse audit comes with its own challenges:

• Not all tips are actionable: for example, if third-party code is involved.
• It doesn't make sense to work on all tasks in parallel. You have to focus on the web performance bottleneck first, or you will see no improvement.
• If you follow all recommendations, you likely fix problems that won’t affect most users.
• Sometimes the effort just cannot be justified by the expected outcome.

Don’t follow the Lighthouse recommendations blindly.

Talk to your developers before creating tickets.

The Web Vitals

Google launched Web Vitals in May 2020. The Web Vitals measure the following three field metrics:

• Largest Contentful Paint (LCP) - Measures how fast the biggest element in the viewport is displayed
• First Input Delay (FID) - Measures how quickly the browser is responding to user interactions
• Cumulative Layout Shift (CLS) - Measures unexpected layout shifts

The Web Vitals can be a good minimum web performance goal for most sites, because they focus on user experience and impact the Google search ranking and Google ad price.

Web Vitals has quickly become the new standard, supported by all web performance tools that measure field data. Because of the obvious business benefits, getting stakeholder buy-in for Web Vitals is easy. The methodology is well documented, and many helpful resources are available online.

However, they are far from being perfect. Only Chromium browsers support these metrics at the moment. Using a real-user monitoring tool, you can measure the Web Vitals for Chrome, Microsoft Edge, and Opera users, but you won’t get data from Safari and Firefox users.

Web Vitals also can’t yet reliably measure the performance of Single Page Applications (SPAs). Google is currently working on new standards and browser APIs to change this, but we don’t know when they will become available.

Custom metrics

Every business is different. Relying only on generic metrics is often not good enough. We recommend using the Performance and Element Timing APIs to create custom metrics for business-critical functionality.

Examples of good custom metrics include:

• Video platform: the main video is ready to play
• Newspaper: the main article is readable
• Search site: the search is ready to accept user input

Creating customer metrics should not be a lot of extra work for your developers, and most browsers and web performance tools support custom metrics.

How fast is fast enough?

Identify your sweet spot

Our goal is not to build the fastest page in the world: sometimes, speed can be in conflict with functionality or features that make our websites great to use and ultimately preferable for visitors. The goal should always be to build the best website for your business and your visitors. The Web Vitals thresholds are great to start with, as they guarantee the full search ranking boost. Being better than good doesn’t give you any additional ranking benefits, but it might increase your conversion rate significantly.

We recommend examining the correlation between your conversion rate and the Largest Contentful Paint. Knowing the business impact of web performance is crucial to defining good thresholds.

How can you reach your thresholds?

Instead of setting goals, we recommend setting a performance budget. A budget is a threshold that you are not allowed to cross.

A good way to define the budget is to look at the worst performance value of the last month. This value will become the new threshold. Then, create tickets to optimize your performance and stay in your sweet spot, without regressing to the worst performance of last month. You update your budget every month by looking at the worst value of the last months, and this means it should improve over time.

Adobe’s Next-Generation Composability

At the Adobe Summit in Las Vegas this year, Adobe presented the next big step in content management with some exciting new services called "Next Generation Composability." The new setup has web performance built-in which makes it a central and major concern when building a website with Adobe’s CMS tools.

Being one of the first partners to implement our website using Adobe Next Generation Composability, we had the opportunity to examine the implementation closely.

A definite highlight is the cloud-native delivery engine, which dramatically improves the time needed to send the website to the visitor. This means the visitor now gets the website delivered from a CDN Edge close to their location, and new content gets actively pushed to the globally distributed edge.

We were also impressed by the out of the box tooling. The combination of automated Lighthouse tests in the CI pipeline and a RUM solution will definitely help to avoid performance regressions.

The provided tools and loading mechanisms provide a great basis for making your website blazing fast, but complex third-party integrations might not be straightforward to implement in an optimized way. We have experimented with many options, like the new browser APIs to prioritize the LCP element or granularly control the loading order, to get the best user experience possible.

Adobe’s Next-Gen Composability Services deliver great web performance out of the gate, but implementing your individual use cases still needs expertise to maintain the performance and make the best decisions supporting conversion and your business. Our expert team is ready to support you and let you leverage our lessons learned and best practices.

How we can support you

Web performance is a complex and dynamic topic that requires full dedication to master. Your developers must be good at a hundred different things, which doesn’t allow them to be excellent at one thing.

As performance has a huge business impact, Cognizant Netcentric invests in a team of experts that provide consulting and create their own real-time user monitoring tool.

We have a fixed-priced offer that includes consulting and all the tools you need to achieve and maintain good performance for your website.

We offer a free 60-minute session with one of your experts if you are interested in learning more about web performance and your current situation. Contact us today to learn more: