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How to get the best results out of client-side and server-side testing and personalization

David Henderson

By David Henderson, CTO

How to get the best results
14th May 2021

Client-side testing and personalization is the most common approach employed by personalization platforms, and the fact that it’s so easily implemented and user-friendly means it remains a valuable solution. But as the web evolves, many businesses are making use of the server-side approach to reap the benefits of faster page load time, increased data security, and more.

Read on for explanations of both types of testing, as well as some of the benefits and drawbacks for each, and discover our take on the optimal approach to client-side and server-side testing.

Client-side testing and personalization

With the client-side testing approach, tests and personalized experiences are rendered from the user’s browser via a piece of Javascript on the client-side.


Client-side testing is easy to use, making it suitable for all stakeholders to do so. It gives you more flexibility, since you can make changes quickly and easily. It does not require advanced technical or scripting skills, and it’s quicker to implement.


Personalized elements load after the main page has loaded, developers have less control, and it doesn’t integrate with IT/web deployment frameworks as changes can be deployed at any time. To comply with the Google Page Experience update and prevent the screen layout changing as it loads, you’ll need to always replace elements on the page with another element of the same dimensions. This restricts your flexibility in changing the page layout.

Server-side testing and personalization

The server-side approach allows retailers to call tests and personalized experiences on the back-end side before the page is rendered.


Server-side testing means the personalized parts of the page load at the same time as the non-personalized parts, and developers have more control. It integrates well with proprietary frameworks. It’s easy to comply with the Google Page Experience update as all changes are made on the server, before it reaches the browser.

There is also increased data security, since sensitive data doesn’t need to be stored client- side. Finally, it cannot be blocked by script blockers, cookie blockers or other privacy protection approaches.


Using this approach requires much more involvement of technical teams and developers, and also means a longer implementation period. It is hard or impossible for marketing or eCommerce teams to make wider-ranging tests and changes, such as making significant changes to the page layout.

What is the best solution?

Look for a personalization platform that can offer a hybrid approach, allowing you to reap the benefits of both client-side and server-side.

Fresh Relevance supports a hybrid approach enabling our clients to use both client and server-side testing and personalization depending on their needs, resources and business goals.

For example, our clients could use client-side tests for initial testing via front-end personalization, because it’s easy to change, quick to iterate and agile. Then once they know which personalized experience performs best, they could switch to a server-side testing tools for faster loading of personalized content and optimal SEO.

Download the Personalization Buyer’s Guide to Identity Resolution for more information about client and server-side testing and personalization.

Download the Personalization Buyer's Guide to Identity Resolution

David Henderson

By David Henderson


As CTO at Fresh Relevance, David leads the dev team. He has been instrumental in designing, building and scaling the platform to help marketers get awesome results by driving sales growth and strengthening customer engagement.