Sander Tigelaar
Head of Web Development and IT
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Client Side vs. Server Side Testing

Advice from Sander Tigelaar, Head of Web Development and IT, on when server-side or client-side testing is more fitting for an experimentation program.
Published:16 October 2023
Reading time:5 minutes

Exploring Server-Side Testing vs. Client-Side Testing: Which Wins the Race in CRO?

In the fast lane of Conversion Rate Optimization (CRO), new buzzwords are always zooming past. One of the hip terms making waves is “server-side testing.” But what’s that all about? And is it always the best choice? Let’s rev up and check out the showdown between server-side testing and its rival, client-side testing, and what Sander, our Head of Web Development and IT, advises.

Server-Side Testing: Deep Dive

Picture this: server-side testing goes down on the client’s home turf – their server. That’s where all the action happens. The backend of the website or app handles the test magic. However, it should not be a goal on its own.

There are some clear perks:

  • No loading glitches: Since tests run on the server, annoying loading hiccups are kicked to the curb.
  • Backend-powered testing: Tests tap into the backend’s brains, making room for bigger, more complex experiments.
  • A smorgasbord of testing options: You can run all kinds of tests, even the ones that scare you a little.

On the other hand, there are also some cons:

  • IT/development tag-along: Server-side tests need the IT or development crew onboard, which might slow things down if they’re swamped or have other VIP tasks.
  • Waiting game: If the dev squad is swamped, your test might be chilling in line for a while.
  • No test vibes for teammates: Roping in the server for tests might not spark the testing enthusiasm in your team.

Client-Side Testing: Speed and Flexibility FTW

On the flip side, client-side testing works like a charm. Tests are carried out in the client’s code; no backstage server action is needed. And guess what?

It’s got some awesome benefits:

  • Speedy setup: No waiting on server updates. You can drop tests like it’s hot and keep the good vibes going.
  • Visual playground: Client-side tests are the go-to for visuals and user experience testing.
  • IT/development independence: You can dance to your testing tune without bugging the IT or dev squad.
  • Warp speed: Quick setup means rapid-fire changes and turbo-charged improvements.
  • Test-tastic mindset: Frequent testing can ignite a fire for testing in your whole team.

And there are some cons:

  • Frontend focus: Client-side tests can’t flex their muscles on backend stuff like testing new product modules or supercharged search features.
  • Loading gremlins: Rare as a unicorn, but there might be an odd glitch when pages load due to client-side tests.

What’s the deal with first-party cookies?

All client-side AB testing tools operate using first-party cookies. Consequently, they remain unaffected by the recent browser changes, such as Chrome’s changes on third-party cookies. Now, if you fancy using a server-side cookie for your AB testing, it’s entirely doable in conjunction with client-side testing. There’s a variety of nifty solutions for tackling this challenge. Here are a couple of examples:

  • You could employ the splitter from a server-side testing solution to furnish some kind of identifier in the front end. It could be a cookie or something nestled in the source code like a JavaScript variable. This helps distinguish which user experience to serve up.
  • Alternatively, you can leverage the user ID (if available) to group users on the front end.
  • Another option is crafting a backend script that utilizes the client-side cookie and generates its own identifier based on that.
  • Or, for the DIY enthusiasts, you can craft your very own server-side splitter, although in most cases, opting for a server-side solution tends to be the smarter choice.

Taking Privacy to the Next Level: Crafting Your Custom AB Testing Solution

Regarding privacy concerns: While transitioning to a server-side approach can offer some benefits, it’s essential to recognize that it doesn’t work like a magic wand for privacy issues. You still need to tread carefully when handling potentially sensitive user information and ensure that your AB tests align with the consent levels provided by users.

Typically, most AB tests focus on enhancing the overall website and don’t delve into individual user profiles. However, it’s crucial to note that many AB testing tools collect their own data. In such cases, it’s imperative for these tools to adhere to the corresponding consent levels.

For those who seek the ultimate privacy assurance, you have the option to craft your custom solution that doesn’t collect any user data. In this scenario, all analytics would be carried out within your dedicated analytics environment, offering privacy as a built-in feature.

Sander’s Wisdom, Head of Web Development and IT

Sander, the head of web development, drops some real talk on this topic. While server-side testing gets the applause, Sander lets us in on a secret: client-side testing can be the cool kid too. He’s all about the speed, flexibility, and rapid improvements of client-side testing. His tip? Ride the speedster lane for quick wins and a never-ending cycle of platform upgrades.

The Final Lap

While server-side and client-side testing have their fan clubs, Sander’s advice is clear: You don’t have to pick just one. Client-side testing brings the speed, flexibility, and test-tastic vibes. Whether you’re into server side, client side, or mixing them up, the finish line is all about the regular rhythm of testing, analysing, and cranking up that conversion power. Let the testing games begin! And if you need some help, especially regarding first-party cookies and privacy, we’re always up for pitching in.

Sander Tigelaar
Head of Web Development and IT
Schedule a CRO audit session
If you're planning optimising your CRO process, one of our experts will discuss your goals and strategies to help you grow
Schedule CRO audit

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