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Front-End Performance Testing and Optimization: All You Need to Know

Aug 28, 2019
11 min read

A modern Internet user is overloaded with information every day. Statistically, there are about 200 million active websites at the moment — not even the longest lifespan would suffice to explore such a plethora of information. 

That’s why the way we experience websites has become just as important as the content they host. ‘The devil is in the details’ is a highly accurate description of the modern web. Low page loading speed or high bandwidth consumption could all be the deal-breakers preventing users from getting to know your company.

To ensure a website visitor sees a flawless version of your website, a project team runs front-end performance testing.

What are its metrics and objectives? How do you choose the right performance testing toolkit? Are there any established practices a QA beginner can use? This post will answer these questions and more. Brace yourself for a full rundown on front-end performance testing.

What is Front-End Testing?

Simply put, front-end testing is a way for QA specialists to assess the performance of a product from a user’s standpoint. 

Compared to server-side testing, there are no controlled environments or back-end monitoring. 

A tester has to fully disconnect from the server-side performance of the project and test it as an independent user.

Several decades ago, front-end testing was not a necessity for QA teams. As pages used to run by simply loading an HTML file, little-to-nothing could go wrong. 

With the adoption of CSS and Ajax, a web page has become a series of external references and stringed operations. Naturally, the room for error expanded, too. 

Now, neglecting front-end performance testing will bring tons of damage in terms of user retention and the extent to which the product adheres to business needs.

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Who Needs Front-End Performance Testing?

While front-end performance testing is usually a part of a QA testing framework regardless of the scale or the size of the project, it’s specifically important for the following types of projects: 

  • E-commerce store managers
    As online shopping websites cover a complete sales funnel — creating an account, browsing the catalog, adding an item to the cart, check-out — a lack of speed optimization and responsivity will directly affect a company’s conversion rates.
  • Development teams for projects with a large mobile user base
    A team needs to ensure that the website works consistently in the environments with low connectivity and keeps a high loading speed on low-end devices.
  • High-traffic website owners
    Front-end performance testing helps monitor bandwidth usage and server throughput. High-traffic website owners will be able to proactively manage crashes and either increase the bandwidth limit during the periods of traffic spikes or remove it altogether.
  • Small business owners that want to get more search ranking exposure
    By tracking advanced metrics, the project management team will be able to find additional ways to optimize the website and make it user-friendly. Small businesses with low marketing and advertising budgets will be the first to benefit from front-end optimization as it’s sought after by most search engines. By capturing a first meaningful paint, time to interact, interaction frame rate, and other advanced metrics, the project team will find ways to make the website more crawler-friendly. Google has declared website speed its priority a long time ago — SME owners need to get on board.

Front-End Performance Testing Tools

To increase the test coverage, reduce the amount of time to complete tests, and improve the cost-efficiency of tests, QA teams rely heavily on technology. A basic front-end performance testing toolkit allows real-time monitoring, offers insights and statistics about the performance of each component of the page, and evaluates the overall performance based on a predefined rule set. 

Naturally, front-end performance testing instruments tend to vary depending on the team or a project. Below is the list of tools most widely used and acknowledged by the tech community. 

1. Lighthouse

Lighthouse is integrated into a Google Chrome. This tool is designed to assess the performance and accessibility of web pages and WPAs.

After collecting performance-related insights, the tool automatically compiles a report with the rich HTML support. Aside from presenting all collected data in a clear, concise way, each report has a section dedicated to potential fixes of detected issues.

Main features:

  • Sharing and viewing audit summaries online;
  • Node.js and command line support;
  • Shell scripts support;
  • Fast page audits (it takes 60-90 seconds to scan the page);
  • Sharing reports on GitHub or saving them as JSON.

Keep in mind that each device you want to run Lighthouse on needs to have a Google Chrome browser client.

2. Web Page Test

QA teams use Web Page Test to run website speed tests for website users from all over the world. Testers get the precise amount of time it takes for a page to load across a wide range of devices — PCs, Mac computers, iPhones, Android smartphones, and tablets. 

The tool records page loading speed and displays the interface in an authentic way. Web Page Test supports low-powered gadgets as well — like Moto G4. 

Main features:

  • A wide range of bandwidth and latency filters;
  • The list of metrics includes ‘First Byte’, ‘Start Render’, ‘First Interactive’ and many others to provide a tester with a multi-faceted view of the website;
  • Comprehensive network waterfall visualization;
  • Continuous web page monitoring.

In terms of interface and navigation, Web Page Test is not easy to use, but it’s one of the most feature-rich platforms for continuous monitoring out there.

3. Pingdom

Pingdom is another platform for real-time front-end performance monitoring. It helps QA specialists get and process data on website loading speed across various locations, devices, or browsers.

Main features:

  • Parallel interaction monitoring;
  • Real-time outage alerts;
  • Continuous page load time tracking;
  • Rich performance data: HTML, CSS scripts, images, and other loaded elements.

Pingdom is a widely used tool in the QA community. Companies like Amazon, Spotify, Netflix, Slack, and other industry giants use it for performance testing. 

4. Httperf

Httperf is a solution for web-server performance management. The tool aims to facilitate the process of designing micro- and macro-scale benchmarks. 

Httperf improves the efficiency of workload generation. The tool provides testers with a full set of metrics for performance management.

Main features:

  • Automatically generated and sustainable server overloads;
  • SSL and HTTP/1.1. protocols support;
  • Integrations with other workload generators;
  • Command line and AJAX testing support.

It’s worth pointing out that Httperf only tests the rendered HTML versions of provided URLs.

5. JMeter

JMeter is a tool for automated front-end testing, with a wide range of supported protocols and languages. The program runs on Java with Swing as it’s graphical API. Testers can start JMeter on all common testing environments — Windows, Linux, and Mac OS. 

The list of protocols that the tool supports includes web (HTTPS, HTTP), web services (XML-RPC, SOAP), databases, directories, message-oriented, and FTP services.

Main features:

  • Open-source license;
  • Easy-to-use interface;
  • Full lightweight component and Swing support;
  • Multi-threaded concurrent sampling is supported;
  • High extensibility.

JMeter runs simulations by imitating a group of users, sending a target request to the server and reporting back to the tester about the functionality and performance on the website.

Benefits of Front-End Performance Testing

As front-end performance testing is connected to client-side issues, its impact is more visible to the end user and directly affects the browsing experience. After having tested the performance of the entire front-end, in theory a QA team should end up with a stable and fully functional build ready to be brought to market.

How exactly does front-end testing improve the performance of the website? What are the goals it helps businesses achieve?

Here’s a list of the most significant benefits front-end performance testing brings to the table.

  • Detecting client-side performance issues
    Most types of testing are focused on examining and optimizing the inner workings of the project — its back-end, server-side activity, etc. Front-end testing is the only way for QA teams to assess the product the way a user would. After having conducted it, the development team will be confident a single interface sequence error does not jeopardize key workflows.
  • Tests are simple and cost-effective
    When it comes to the front-end application testing toolkits, most solutions are free to use. Moreover, monitoring is one of the key activities in front-end performance testing — a QA doesn’t have to spend that much time writing scripts compared to other types of testing.
  • Improved quality of user interactions
    For the majority of web users, speed is the main benchmark a front-end performance testing mainly focused on. The company will be able to increase the effectiveness of user journeys by reducing the page load time, ensure all the content is displayed as intended, and the webpage has a unified look and feel across all browsers and devices — and all of this exponentially increases the quality of visitors’ interactions with the website.
  • Missing out on front-end end testing does lots of damage
    Factors like page load speed and usability are crucial for ranking algorithms — thus, by missing out on optimizing those benchmarks, you lose a share of potential visitors. Moreover, a low-performing user interface will hurt your lead generation funnel if one or several key workflows are comprised, including check out, adding an item to a shopping cart, creating an account, etc.

All of these benefits make a strong case for conducting thorough front-end performance testing.

Front-End Performance Optimization

While fully optimizing a website’s front-end is a continuous process that requires both time and effort, there are several straightforward practices. It doesn’t take too much time, money, or skill to implement these tips, but the positive impact of the changes listed below will be evident right off the bat.

1. CSS Performance Optimization

CSS files are crucial as they help add a clean and professional style to an HTML document. However, the truth is that a fair share of CSS options require HTTP requests. If a website is overloaded with cascading style sheets, its loading speed will plummet.

In order to avoid performance pitfalls, a front-end and designer has to detect and remove all bloated CSS documents. Another practice worth following is that of replacing import directive, commonly used to add an external spreadsheet to the page by link tags. 

The second approach is preferred as it doesn’t block parallel downloads.

2. Reducing External HTTP Requests

Depending on the nature of an external HTTP request, its negative impact on the loading speed will vary. It’s best to keep the number of such requests to a bare minimum.

What can be cluttering your webpage?

JavaScript-empowered content and images are the most widely used elements that require external requests. Be sure to remove all content and plugins that don’t directly contribute to user experience quality.

3. Prefetching

Prefetching is a proactive way to manage user experience as it loads an image, links, and other content before a visitor clicks on it. 

There are three standard prefetching methods:

  • Prerendering;
  • Link prefetching;
  • DNS prefetching.

Thanks to prefetching URLs, a user will be able to access web pages faster (as the page’s JS file will be fetched before a user even chooses it).

Prefetching is easy to implement. Adding a ‘rel=’prefetch‘ to the HTML file is all it takes.

4. GZip Compression

This technique is especially important for users who don’t use CDN services (these tools offer built-in compression). GZip compression helps website managers to reduce the size of their HTML JavaScript files, and stylesheets. It has been a recommended practice both by GTMetrics and Google. 

The downside your team will have to put up with is that GZip compression will not run on older browsers. The range of clients it supports includes:

  • IE 5.5 and higher;
  • Opera 5+;
  • Mozilla Firefox 0.9.5+;
  • All versions of Chrome;
  • All versions of Safari.

By implementing GZip file compression, companies will reduce the size of files shown on a page and its overall load time. 

5. Image Optimization

It’s tempting to upload HD content to the website. However, keep in mind that high-resolution images might get in the way of rendering. 

How do you optimize images with no quality loss? First off, examine the file and delete all irrelevant data — camera specs, date, location, etc. 

Another way to optimize images is by using dedicated tools. There are dozens of options to test — here are a few:

6. Advanced Performance Metrics Monitoring

There’s a common saying that goes: ‘If you can’t measure it, you can’t manage it’. This is absolutely true for performance testing. Basic metrics like page load time provide developers with little insight on user experience. 

To get a better idea of your front-end performance, consider setting and monitoring advanced benchmarks. Here are a few metrics professional QA specialists usually track during continuous front-end performance testing:

  • Speed Index — an average time it takes to load all blocks of the page;
  • First Contentful Paint — this gets triggered when a section of content is defined in the Document Object Model;
  • First Meaningful Paint — gets triggered by an above-the-fold layout change that’s bigger than the rest;
  • Input Latency — a delay between receiving and displaying the signal;
  • Time to Interactive — measures the amount of time needed for a page to become fully interactive. The ‘interactivity’ is defined by the following conditions — useful content has been displayed, event handlers for most visible elements have been registered, the page response time is not higher than 50 milliseconds.

Optimizing these metrics will prove that a website will be responsive even for low-end device users. 

All of these tips are easy to implement even for website managers with little-to-no programming experience.

Front-End Performance Testing with PFLB

Performance testing is a crucial stage that determines whether or not a product is ready for a release. That’s why it’s crucial to have a team of professional QA specialists on board. 

At PFLB, you can entrust the front-end performance testing of your app to certified professionals. We use advanced tools to automate and streamline testing.

We assist the development team throughout the entire product life cycle. Our specialists will consult your company’s technical department in order to create an optimal testing strategy. Moreover, we’ll adopt the project management framework that your office uses in order to synchronize all operations between teams. 


Performance is crucial when it comes to creating a successful website or building high-performance software. Many developers use powerful gadgets for daily work and have an outstanding Internet connection — but all that speed is often taken for granted. 

By definition, front-end testing is designed to provide ways for users to enjoy browsing through a website on a cell phone, in a subway with poor connection, and on low-end devices. 

The good news is, front-end performance testing strategies are usually straightforward, and most tools are available for free usage. Compared to other types of software testing, assessing the front-end is not too expensive or time-consuming. 

Yet, it’s highly important to assign front-end performance testing to a team of professional testers. To be sure your project is handled by first-rate professionals, reach out to PFLB. As a quality assurance services provider, we have completed dozens of testing projects for small- and large-scale projects.
Take a look at our full list of services to find out how PFLB can contribute to your project or take a look at our test cases to see the front-end testing example reel. To discuss the testing of a website or an app, contact us — we’ll get back to you shortly with a list of our ideas on your project.

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