Server-side testing vs client-side testing: What’s your solution for the post Google Optimize era?

“Nothing is so painful to the human mind as a great sudden change.” - Mary Shelley

Change can be unsettling, especially when it’s sudden and unplanned. This sudden shift often leaves us feeling disoriented and unsure of how to proceed, pushing us far outside our comfort zones.

I think this is precisely how many companies felt when Google announced the discontinuation of Google Optimize in 2023. Google Optimize, a cornerstone tool for A/B testing and personalization, and its sudden phase-out pushed companies to scramble for alternatives racing against the clock to adapt to this unexpected change.

With little warning, businesses had to quickly find new A/B testing tools or develop in-house solutions that work with Google Analytics 4 (GA4). This shift forced many to rethink their CRO strategies and technology stacks.

Businesses generally have two options: server-side testing and client-side testing. Server-side testing, used by larger companies, offers greater accuracy and control but requires more resources.

Client-side testing tools, like Google Optimize, are generally easier to set up and use, making them popular among mid-sized companies; though they often suffer from performance and data accuracy issues. Consequently, mid-sized companies face greater challenges in finding suitable alternatives.

Client-side testing tools are popular for their ease of use and quick setup, especially when integrated with a headless CMS to run fast experiments. Despite these benefits, several drawbacks can affect the accuracy and reliability of your tests.

As Ruben De Boer, Conversion Manager at Online Dialogue, points out "The relative ease of use of client-side also has disadvantages”. He emphasizes that the scope of client-side testing is generally limited to design elements like colors, texts, layout and elements. While this may suffice for some organizations, Ruben notes that “at some point, you want more possibilities.”

Security is another major concern with client-side testing. As Ruben explains "With client-side testing, an external script from your tool has access to your website and data, which brings risks,” especially in secure areas like login pages or where customer data is handled.

In addition to security risks, client-side testing faces other limitations:

• Flicker effect: Visitors often see the original page for a moment before the test variation loads, which can negatively impact user experience.
• Cookie management: Client-side tests depend on cookies to track user behavior and assign test variants. However, privacy restrictions in browsers like Safari can limit the effectiveness and lifespan of these cookies. This can lead to inconsistent data, as cookies may not persist across sessions or be cleared, affecting the reliability of test results.

On the other hand, client-side experimentation tools are easy for marketers to implement and use.

Server-side testing is often hailed as the ultimate solution for overcoming the limitations of client-side experimentation. Here’s why:

• Eliminates flicker effect: Variants are loaded directly from the server, ensuring a smooth user experience without interruptions.
• Faster loading times: With the test variations loaded from the server, latency is reduced, leading to quicker page loads and better performance.
• Quicker implementation: Winning variants can be rolled out faster since they’re already live on the server.
• Ideal for complex tests: This method is particularly effective for testing intricate features, app functionalities, or major redesigns.

However, it’s worth noting that server-side testing can be complex and resource-intensive, often requiring significant technical support, which makes it more accessible to larger organizations with the necessary infrastructure.

While server-side testing is often seen as the gold standard in experimentation, this doesn’t mean it’s always the better choice compared to client-side testing.

What's the saying? Horses for courses right?

As Jay Lansdown, Experimentation Lead at New Look notes ”Client-side experimentation can get a bad rap in the experimentation community," yet it remains a valuable tool in many contexts.

Server-side testing is often praised for its efficiency and effectiveness, particularly with agile workflows.

However, it’s not always the best choice for every scenario. Client-side testing offers distinct advantages, especially for dynamic and short-lived content like marketing messages or copy testing. As Jay Lansdown highlights, “Client-side experimentation is perfect for dynamic content that needs to be adjusted frequently,” allowing for quick updates and immediate feedback.

In the end, what works best depends on your specific goals and audience. Both client-side and server-side testing have their place, and the choice between them should be guided by what best suits your particular needs and context.

While these two testing methods offer significant benefits, they also bring new challenges, particularly in integrating them with existing systems.

Tool integration is a major issue, with only 13% of companies achieving full integration of tools for experimentation, data, and KPIs.

This creates a gap that mid-sized companies often struggle to bridge. Managing separate systems for different functions can lead to scattered data and inefficiencies. Without a unified system, it’s challenging to ensure smooth data flow and cohesive insights, impacting decision-making and optimization.

A promising trend in digital marketing is the rise of headless CMS platforms that include built-in optimization capabilities. These systems, often called conversion-centric CMS, offer A/B testing and personalization directly within the CMS, allowing businesses to manage content and run optimizations all in one place.

By handling A/B testing and personalization server-side, these CMS platforms offer the performance and security benefits of server-side testing, without the complexity. They are easy to use, even for non-technical teams, and cost-effective, making them a great fit for mid-sized companies. While they might not have every advanced feature, they focus on the tools that drive engagement and boost conversions.

In the end, changes like Google Optimize’s discontinuation may be challenging, but they also open doors to new and better solutions. By understanding the strengths and limitations of both client-side and server-side testing, and by considering innovative solutions like a conversion-centric headless CMS, companies can better manage these changes and come out stronger.

Learn more about A/B testing with Prepr CMS to see how it can transform your optimization strategy.