"Web performance" is often also referred to by its contracted form "webperf." In English, we talk about WPO, for "Web Performance Optimization." As its name suggests, it aims to measure the level of web performance. Not very clear for a novice, is it? To be precise, we are talking about technical performance (loading speed), not commercial performance (conversions, RPM, etc.). The two are very different but are sometimes confused.
Definition of web performance
If we were to give it a definition, web performance would thus be the "technical discipline aimed at ensuring fast display and good fluidity of web pages in browsers, during their loading and throughout their use." This is the definition we have chosen in our webperf glossary and which seems to us the most explicit and accessible for non-technical profiles.
What are the stakes of web performance?
Why do we do web performance? A seemingly simple question, but one with multiple answers. Let's look together at the benefits of offering a fast site to internet users.
A better User Experience
Improving the speed of a site's pages means ensuring that a maximum number of users can access them regardless of their access conditions (Internet connection, device power, web browser, etc.). For the majority of visitors, this translates into reduced waiting time and better fluidity when viewing content pages or using online tools. User Experience is thus much more qualitative on a website optimized for web performance.
Multiple studies and concrete cases have demonstrated the positive impact of performance optimization on indicators such as conversion rate, bounce rate, or even revenue. Amazon, which was a pioneer in the field, estimates, for example, that every 100-millisecond gain in loading time allows a 1% revenue gain. Other cases highlighted by Yelp, Mozilla, or Walmart show even more spectacular gains. And this is without mentioning the impact related to increased loyalty, which other reports highlight elsewhere.
In the more specific context of AdWords campaigns (or others), optimizing landing pages can have a significant impact on return on investment. This can considerably reduce the acquisition costs of new customers and prospects.
Improve its visibility in Google
The second reason why web performance is popular is linked to its biggest ambassador: Google. To reduce its costs related to page indexing, the number 1 search engine is indeed pushing site publishers to improve their page loading times. The " crawl " phase, essential for updating the results pages for millions of daily queries, is thus less impactful for the American company, whose data centers have a major impact on the electricity bill.
Still on Google's side, fast sites also allow for faster display of ad spaces. However, Google's main business remains online advertising, via its leading platform Google Ads. These are the 2 reasons why Google pushes site publishers to improve their loading times through its dedicated tool: Search Console. The " Page Experience " section includes a " Core Web Vitals " component that has expanded significantly over the last 5 years.
Web performance is thus officially an SEO ranking criterion, even if its weight within the ranking algorithms obviously remains less than that of traditional factors such as authority linked to netlinking and content quality.
Reduce hosting costs
By reducing the number of http requests, the weight of static resources, and the need for costly server-side calculations (PHP script execution, SQL queries, etc.), web performance optimization can reduce server load, sometimes very significantly.
This translates into increased speed, especially during peak loads and periods of high demand (like a TV appearance). If the difference is significant, it can also be an opportunity to downgrade the server configuration by opting for less powerful hardware in terms of processor and RAM (see our vision of performant hosting).
For a high-traffic site hosted on a dedicated server or a large VPS, the difference in hosting costs can be really interesting, and alone justify a web performance optimization project.
Save the planet from global warming?
This third part remains a question because, as web performance specialists, we really want to believe it. A site whose loading times have been optimized will necessarily be lighter and less resource-intensive than a classic equivalent site (both for hosting and for the user). It will thus generate fewer greenhouse gas emissions, which will ensure a lower carbon footprint. We know, however, that in the digital world as a whole, the web is only responsible for 1 to 2% of global emissions.
If we can contribute to making the web better, it is not our work as experts that will save the planet from irreversible global warming.
How is web performance measured?
As in any technical field, having performance indicators is essential to compare different sites or evolutions over time. Similar to the automotive world where a car's performance can be measured in torque, horsepower, top speed, or 0-60 mph time, there are dozens of ways to calculate the webperf level of a web page.
What are the most relevant indicators?
TTFB: Server response time
Some indicators have been used for as long as we've talked about webperf. This is the case for TTFB (Time to First Byte), which measures the time it takes to complete a full round trip between the browser and the server where the visited site is hosted. Simple to calculate, it is ideal for addressing web performance issues related to hosting (data center too far away, inadequate processor or RAM, lack of caching system, poorly configured SQL databases...).
Speed Index: Perceived speed
The other metric that has retained its full meaning over the years is the Speed Index, which measures the time it takes for the visible area of the page (often referred to as the viewport) to load completely. To do this, it is necessary to perform video capture, which is both complex and expensive to implement. This is why not all tools offer it, but also why the indicator can sometimes vary significantly depending on the measurement tool used.
What are Core Web Vitals?
Google, again, introduced in 2020 a set of metrics called “Web Vitals”, including 3 “Core Web Vitals” that have since become the standard. Each aims to estimate the performance level of a web page from a specific angle. Together, they are intended to provide a comprehensive view of a page’s performance level, and even a site’s when averages are calculated, as Google does with its origin reports. Here are these 3 indicators:
LCP
Acronym for “Largest Contentful Paint,” this performance metric measures the time it takes for the main visible element of the page to load. This is often an image, but can also be headings or text blocks. A good LCP should be less than 2.5 seconds, and should never exceed 4 seconds.
FID
Acronym for “First Input Delay,” this performance metric measures the time it takes for a page to become smoothly interactive. It is heavily impacted by JavaScript, and particularly by third-party scripts. To be considered good, it should be less than 100 milliseconds. Above 300 milliseconds, it is considered poor.
CLS
Acronym for “Cumulative Layout Shift,” this performance metric measures a page’s ability to provide an interface whose elements remain stable over time. No visual shift, vertical or horizontal, should occur during resource loading. It is measured without units, with thresholds of 0.1 to be good and 0.25 at maximum.
The 3 other metrics in the “Web Vitals” suite are FCP (First Contentful Paint), which measures the time it takes for the first visible element of the page to load, TTI (Time to Interactive), which measures the time it takes for a page to become interactive for the user, and Speed Index, which was previously presented.
Is your site as fast as your visitors expect?
What tools are used to measure web performance?
There are 2 main families of tools that allow you to evaluate the performance level of a page or site: synthetic testing tools, which provide access to so-called “lab” data, and Real User Monitoring (RUM) tools, which provide access to field data, i.e., data observed by real users during their browsing sessions on the site in question. Their operation is very different, giving each its own advantages and disadvantages.
Synthetic measurement tools
There are dozens of tools dedicated to calculating web performance. Some are free, others are paid, but the majority are available in both free and paid versions, with limitations on features and/or test volumes. They all offer at least information on traditional metrics and Web Vitals. What sets them apart is their ability to provide relevant recommendations based on a more or less qualitative and up-to-date benchmark. Here is a selection of the most popular, keeping in mind that there are other equally relevant ones.
PageSpeed Insights
This is the most popular tool, which many mistakenly believe is what Google takes into account in its algorithm. Very easy to use, it provides fairly basic recommendations for improving the average score, calculated on a scale of 100.
Lighthouse
Another essential tool in the Google ecosystem, it is accessible directly via the Chrome browser developer tools through an extension. The recommendations are the same as in Page Speed Insights, with additional sections dedicated to accessibility, SEO, or applications.
GTmetrix
An independent and paid tool, GTmetrix offers more advanced analysis features than Google's tools. It is also usable for regularly monitoring sites, thus tracking optimization work and detecting potential regressions.
WebPageTest
Webpagetest is a sophisticated and technical tool ideal for understanding a site's performance issues. It is particularly highly regarded for its detailed visualization of the loading waterfall, and for its multiple features in its paid version.
Real User Monitoring tools
RUM-type SaaS tools are fewer and less popular, and for good reason: they require deployment before they can provide data, and their operation involves significant costs that are reflected in the selling price of existing packages. This was without counting on Google, yet again, which collects, consolidates, and freely shares the most important field database for web performance: the Chrome User Experience Report, or CrUX. Its French translation is rarely used: Rapport d’expérience utilisateur Chrome.
What is CrUX?
CrUX gathers data collected by users of Google Chrome and Microsoft Edge browsers who are signed into a Google account. This is done automatically and transparently, without any action from users or site publishers. The result is a goldmine that Google uses both in its tools for publishers (Search Console, Lighthouse, Page Speed Insights) and in its ranking algorithms.
CrUX data is thus literally your web performance scores in Google's eyes. This is a first: since the disappearance of Pagerank, Google has never shared data used as-is within its ranking algorithms. While their impact remains negligible for most queries, it remains one of the few levers that can be improved by visualizing the impact from Google's side.
What other RUM tools for web performance?
If you want to collect information from your real users without being limited to browsers supported by CrUX, there are several solutions: SpeedCurve, Raygun, Contentsquare, or appYuser. Keep in mind that they will all be paid, with plans or contracts based on the volume of page views monthly or annually. For large e-commerce sites, this can quickly represent a significant budget. Solutions linked to Application Platform Management (APM) can be relevant for reducing costs as part of a comprehensive monitoring strategy (frontend and backend).
How to improve web performance?
Web performance is a technical discipline that must be considered very early in the site creation process, just like accessibility, SEO, or security. To be sure of having a fast-loading site, it is therefore essential to address the issue from the drafting of the specifications. Technical choices regarding the stack (framework, SSR solution, server architecture, etc.) and specific developments can then be adapted to achieve the objectives set in terms of average page weight or any other performance indicator (FCP, Speed Index, Blocking Time, etc.).
Turn to a web performance specialist
Obviously, this approach is still rare and most websites continue to be put into production without any focus on web performance, even at major renowned web agencies. Optimizing web performance to achieve objectives set late is then often a challenge, especially for development teams who often do not master the subject.
The solution is to turn to specialists to carry out a performance audit, or if possible, a performance optimization. We offer this type of service, with always very interesting gains thanks to tools and methodologies developed over years of experience. The distribution of optimizations is faithful to the Pareto Principle, with 80% of classic optimizations and 20% more specific ones resulting from technical choices specific to each client. It is in this last segment that an expert's perspective brings maximum added value, allowing ambitious objectives to be achieved.
Improve the skills of your teams or your provider
The other solution is to address the problem at its source: front-end developers. Whether through watching free videos, reading articles and resources like Web.dev, or through in-depth training, the idea is to lay the groundwork for them to acquire the right reflexes and habits. All of this should be supplemented by regular monitoring, as the technical environment evolves very regularly: CSS, HTML, and JavaScript standards, web browsers, frameworks, tools, SaaS solutions, etc.
This is the best way to create a performance culture within technical teams, but also transversally on the business, marketing, or UX/UI side. All these profiles indeed have a role to play in improving page speed, whether through their development work, the choice of third-party tools, or the design of interfaces and tools.
What can we say to conclude?
As you will have understood by reading this article: web performance is a subject that is as vast as it is specialized. The KPIs, tools, and methodologies exist but remain generally poorly understood and mastered. Even front-end developers, who use the same languages and tools daily as web performance experts, are still too numerous to ignore the impact of certain choices on loading times or page interactivity. It is they who, day after day, through their freelance or web agency work, contribute to creating the web as we know it, with the aberrations we have to face.
Just as SEO gave birth to SEO agencies, we took the gamble of creating the first agency specializing in web performance. If you wish to undertake projects in this field, do not hesitate to contact us: our sharp expertise is ideal for prioritizing an optimization roadmap, making architectural and tool choices, or helping your teams develop their skills. We are here to build a faster web together that meets the expectations of your customers and visitors.
