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Does split testing slow down my site?

Yes, slightly. When a visitor lands on your website while there are tests running, Nelio A/B Testing scripts kick in and perform the following actions:

  1. Check if the current page is under test
  2. If it is, check if the visitor participates in the current test
  3. If they do, determine which variant they’re supposed to see
  4. If they’ve been presented variant A and they’re supposed to see another one, redirect them to the appropriate variant

Steps 1 to 3 are extremely fast and run in parallel while the page is loading, and therefore they barely have a performance penalty. Step 4, on the other hand, is the slowest: if the visitor was supposed to see a different variant than the one they’ve been originally presented (usually, the control version), Nelio A/B Testing has to trigger a JavaScript redirection to send the visitor to the appropriate variant and, thus, the page loading process starts from scratch again.

Add testing query arg to speed up page loading times

As you may already know, alternative content is loaded by appending a special query arg (nab) in tested URLs that tell WordPress which variant should be loaded. When a visitor is on a page in your website (be it under test or not), our plugin will look at all the internal links it contains and, if a link points to a tested page, it will add the appropriate nab query arg to said link. This way, if the visitor clicks on the link to browse to a tested page, the browser will request the correct variant, thus making step 4 unnecessary.