Howuku is lightweight and complete web analytics to help you track user interaction, boost engagement, and improve conversion rates.
Get started for free
Faster result, better ROI. Finally, you can run experiments, personalize, and publish new updates directly to your website without going through your dev team.
Explore AI A/B Testing
What is
Min read

What is Client-Side and Server-Side Web Experimentation? A Simple Explanation.

LiRou Chua
July 4, 2023
5-star rating
Reviews on Capterra
What is Client-Side and Server-Side Web Experimentation? A Simple Explanation.

As we venture into the expansive realm of web experimentation, two commonly encountered yet mystifying terms stand in our path - "client-side" and "server-side" methods. They fill many conversations in web testing circles but can induce some head-scratching. What do these terms signify? And when should you lean towards one over the other? Let's embark on this exploration journey to decode these web phenomenon!

Client-Side Web Experimentation: A Closer Look

At its core, client-side web experimentation revolves around making changes within the user's browser. The modifications are implemented using JavaScript after the page has loaded. Hence, the control and treatment versions of your webpage are determined directly on the user's browser.

For instance, let's say you're A/B testing a new color theme for your website's call to action (CTA) button. In a client-side setup, the JavaScript would manipulate the webpage in real time, showing some users the original CTA button, while others see the new color theme. The client-side method shines in its simplicity and speed of design changes.

However, this method comes with a catch - it might negatively impact your webpage's load time due to the JavaScript. Plus, it can limit you to front-end changes only, so no dabbling with algorithms or backend logic.

Server-Side Web Experimentation: The Other Side of the Coin

On the other hand, server-side web experimentation makes changes directly on the server before the webpage is even sent to the user's browser. Let's look at a real-world example: 

Suppose you want to test an entirely new recommendation algorithm on your e-commerce site. With server-side experimentation, the different recommendation algorithms (original and treatment versions) would be implemented directly on your server. When a user accesses your site, they receive a version determined by the server, and the user's browser doesn't have to do any additional adjustments.

Opting for this method allows for much deeper changes. Altering back-end logic or databases? Server-side experimentation has got you covered. Plus, it often results in faster load times, as there’s no need for browser-side manipulations.

But, tread carefully – server-side changes often require more development resources, may involve more risk and are generally more complex.

Client-Side or Server-Side: How to Choose?

Deciding between client-side and server-side web experimentation ultimately hinges on your specific needs, resources, and testing goals. Here's a deeper dive into factors to help you make the best choice:

1. Complexity and Depth of Changes

Consider the depth of changes your experiment requires. If you're contemplating simple, front-end changes such as adjusting button colors, text fonts, or image placements, then client-side testing is both sufficient and quicker.

However, if your experiment demands more profound changes that touch on back-end logic, like modifying a recommendation algorithm, testing a new checkout process, or settling on new database structures, then you'd be better off with server-side testing.

2. Resources and Expertise

The next aspect to consider is the available resources and expertise. Client-side testing is generally quick to set up and doesn't require much technical know-how, making it ideal if you lack developer resources or your development team has a significant workload.

On the contrary, server-side testing often requires considerable resources and expertise because it involves making changes to the backend code of your website or application. It's worth opting for if you have the technical bandwidth and the experiment could significantly impact your results.

3. Load Time and User Experience

In client-side testing, the page loads before any changes are made, this could lead to a visible shift in page elements or slower load times which might affect user experience.

In server-side testing, users experience quicker load times because all changes are made before the page loads, providing a smoother experience.

4. Data Sensitivity and Security

When dealing with sensitive data or changes that might impact data security, server-side testing is considered safer. In client-side testing, all changes (including those involving sensitive data) are made in the browser, making it less secure and less suitable for experiments involving data privacy.

5. Long-term Changes

If the changes you plan on testing might become long-term modifications to your website or application, server-side testing is superior. The changes are made directly to the page source, which gives a more accurate representation of how the changes will function and impact user behavior if implemented.

Common Use Cases of Client-Side Web Experimentation

1. Web Design Changes

Want to experiment with your webpage’s appearance? Client-side testing excels in trying out visual modifications like color schemes, fonts, images, button placements and sizes, and headlines.

2. Content Variations

Client-side testing is also perfect for testing different copies of your ad campaigns, blogs or website content to see what resonates better with your audience.

3. UI/UX testing

For exploring and optimizing the user journey or user interface (UI) elements on your site ranging from navigation menus to form fields, client-side testing makes it straightforward.

Common Use Cases of Server-Side Web Experimentation

1. Back-End Functionality Changes

If you're looking to test changes in the core website functions or system performance, then server-side testing is ideal. For instance, you could test new recommendation algorithms or speed optimisation techniques.

2. Customer Journey Optimizations

Server-side testing can help optimize the customer journey, like testing different sign-up processes or shopping cart functionalities, which often involve complex backend operations.

3. Product Features

If you're developing a new feature or functionality on your website or application and need to test its performance and effect on user behavior, server-side experimentation can offer versatile and meaningful insights.


In conclusion, the choice between client-side and server-side testing doesn't boil down to 'one's better than the other'. Each methodology serves different needs. Understanding the requirements of your experiment, your resources, and what you hope to learn will guide you to the right choice.

Supercharge your startup growth with Howuku

Start your 14-day free trial today.