8min read

Client and Server-Side A/B Testing – The Best of Both Worlds

We’re enriching our conversion rate optimization platform with a server-side A/B testing solution. What is server-side A/B testing, you ask? It’s the subject of an announcement of ours that will make anybody who’s passionate about experimentation pretty excited…because it means they can now test any hypothesis on any device.

No matter if you want to test visual modifications suggested by your marketing team or advanced modifications tied to your back office that are essential in the decision-making process of your product team, we’ve got the right tool for you.

What’s the difference between A/B testing client-side, and A/B testing server-side?

Client-side A/B testing tools help you create variations of your pages by changing the content sent by your server to internet users in the web browser. So, all the magic happens at the level of the web browser (called ‘client’ in the IT world), thanks to JavaScript. Your server is never called, and never intervenes in this process: it still sends the same content to the internet user.

Server-side A/B testing tools, on the other hand, offload all of this work from the web browser. In this case, it’s your server that takes on the task of randomly sending the internet user a modified version.

4 reasons to A/B test, server-side

Running an A/B test server-side has many advantages.

1. Dedicated to the needs of your product team

Client-side A/B testing is often limited to surface-level modifications. These refer to visual aspects, like the page’s organization, adding or deleting of blocks of content or modifying text. If you’re interested in deeper-level modifications related to your back office – for example, reorganizing your purchase funnel, or the results of your search or product sorting algorithm – it’s a bit more complicated.

With server-side testing, you have a lot more options to work with, since you can modify all aspects of your site, whether front-end or back-end. With server-side testing, you have a lot more options to work with, since you can modify all aspects of your site, whether front-end or back-end.

All of this is possible because you remain in control of the content sent by your server to your website visitors. Your product team will be overjoyed since they’ll gain an enormous amount of flexibility. They can now test all kinds of features and benefit from a truly data-driven approach, to make better decisions. The price of this increased flexibility is the fact that server-side testing requires your IT team to get involved in order to implement modifications. We’ll get back to this later.

Your product team will be overjoyed to test all kinds of features

2. Better performance

Poor performance – loading time or the flickering effect – is often the first criticism made about client-side A/B testing solutions.

In the most extreme cases, some sites only add the JavaScript tag to the footer of the page to avoid any potential impact on their technical performance. This policy automatically means excluding using any client-side A/B testing tools, since a ‘footer’ tag is often synonymous with flickering effect.

When using a server-side A/B testing tool, you don’t have any JavaScript tag to insert on your pages, and you’re in control of any potential performance bottlenecks. You also remain responsible for your company’s security policy and the adherence to internal technical procedure.

3. Adapted to your business’s rules

In some cases, your A/B test might be limited to design-related modifications, but you have to deal with profession-specific constraints that make it difficult to interpret a classic A/B test.

For example, an e-commerce merchant might understandably wish to take into account canceled orders in their results, or else exclude highly unusual orders which skew their stats (the notion of outliers).

With a client-side A/B test, a conversion is counted as soon as it occurs on the web browser side when the purchase confirmation page loads or a transaction event type is triggered. With a server-side A/B test, you remain in complete control of what is taken into account, and you can, for example, exclude in real time certain conversions or register others after the fact, by batch. You can also optimize for more long-term goals like customer lifetime value (LTV).

4. New omnichannel opportunities

Server-side A/B testing is inseparably linked to omni-channel and multi-devices strategies.

With a client-side solution – which relies on JavaScript and cookies – your playing field is limited to devices that have a web browser, whether it’s on desktop, tablet or mobile. It’s therefore impossible to A/B test on native mobile apps (iOS or Android) or on connected objects, those that already exist and those still yet to come.

On the other hand, with a server-side solution, as soon as you can match up the identity of a consumer, whatever the device used, you can deploy A/B tests or omnichannel personalization campaigns as part of a unified client journey. Your playing field just got a lot bigger 🙂 and the opportunities are numerous. Think connected objects, TV apps, chatbots, beacons, digital stores…

Use cases for server-side A/B testing

Now, you’re probably wondering what you can concretely test with a server-side solution that you couldn’t test with a client-side tool?

Download our presentation: “10 Examples of Server-side Tests That You Can’t do With a Client-side Solution”

Included are tests for sign up forms, tests for order funnels, tests for research algorithms, feature tests…

How can you put in place a server-side A/B test?

To put a server-side A/B test in place, you’ll need to use our API. We’ve described below in general terms how it works. For more information, you can contact our support team, who can give you the complete technical documentation.

When an internet user lands on your site, the first step is to call our API to get a unique visitor ID from AB Tasty, which you then store (ex: cookie, session storage). If a visitor already has an ID from another visit, you’ll use this one instead.

On pages where a test needs to be triggered, you’ll then call our API passing in parameters the visitor ID mentioned above and the ID of the test in question. This test ID is accessible from our interface when you create the test.

As a response to your API request, AB Tasty sends the variation ID to be displayed. Your server then needs to build its response based on this variation ID. Lastly, you need to inform our data servers as soon as a conversion takes place, by calling the API with the visitor ID, and data relevant to the conversion, like its type (action tracking, transaction, custom event…) and/or its value.

Don’t hesitate to use our expertise to analyze and optimize your test results thanks to our dynamic traffic allocation algorithms, which tackle the so-called ‘multi-armed bandit’ issue.

As you’ve seen, putting in place a server-side A/B test absolutely requires involvement from your tech team and a change in your work routine.

While client-side A/B testing is often managed and centralized by your marketing team, server-side A/B testing is decentralized at the product team or project level. While client-side A/B testing is often managed and centralized by your marketing team, server-side A/B testing is decentralized at the product team or project level.

Should you stop using client-side A/B tests?

The answer is no. Client and server-side A/B testing aren’t contradictory, they’re complementary. The highest performing businesses use both in tandem according to their needs and the teams involved.

  • Client-side A/B testing is easy to start using, and ideal for marketing teams that want to stay autonomous and not involve their head of IT. The keyword here is AGILITY. You can quickly test a lot of ideas.
  • Server-side A/B testing is more oriented towards product teams, whose needs involve more business rules and which are tightly linked to product features. The keyword here is FLEXIBILITY.

By offering you the best of both worlds, AB Tasty become an indispensable partner for all of your testing and data-driven, decision-making needs.

Don’t hesitate to get in touch to discuss your testing projects – even the craziest ones!

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