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Frequently Asked Questions in Optimizely Classic: General questions

This article is about Optimizely Classic. If you're using Optimizely X, check this article out instead.
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  • Optimizely Classic

  • Find answers for general frequently-asked questions about Optimizely Classic

General questions 

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How will Optimizely Classic affect my pageload times? Will my site lag? 

The short answer: no. Your site shouldn't lag, and any delay to pageload times should be undetectable to the human eye.

We understand that even small increases in page load times must be taken seriously, so we do everything we can to make sure that Optimizely's impact on your page is as small as possible.

There are two Optimizely endpoints that receive web requests from your pages while an Optimizely Classic experiment is running:

  1. Your Optimizely JavaScript (referred to in your snippet) file is downloaded from either of our CDN providers, Akamai or Edgecast, based on optimal proximity and reliability
  2. Your visitors' browser sends tracking requests to Optimizely

Your Optimizely JavaScript file is referred to in your Optimizely snippet and is downloaded by your visitors' browsers at the very beginning of the page load process. It weighs in at ~35kb, is entirely static, and will be cached in your visitors' browsers after the first request. It's also hosted on Akamai and Edgecast, our global CDN providers, so there is no load-time dependency on Optimizely's servers.

The Optimizely JavaScript file download occurs in parallel alongside other JavaScript and CSS files on your site and should take roughly 80-100ms to complete in North America.

Your visitors' tracking requests are made when your visitors land on a page containing your Optimizely snippet. This is how Optimizely collects analytics on your conversion goal performance. These requests are asynchronous, non-blocking, and only occur for visitors that have been placed in at least one experiment. They should have no effect on your page load time.

How does Optimizely Classic affect my search ranking or SEO (Search Engine Optimization)? 

Google permits and encourages A/B testing and has stated that performing an A/B or multivariate test poses no inherent risk to your site’s search rank. However, it is possible to jeopardize your search rank by abusing an A/B testing tool for purposes such as cloaking. We have more in-depth information in our SEO and search ranking article.

What version of jQuery does Optimizely Classic use? 

Optimizely Classic uses jQuery version 1.11.3 by default.

If you elect to use your own version of jQuery instead of the version bundled in your Optimizely JavaScript file, version 1.4.2 or later is required for compatibility.

How do I find more information about the Optimizely API? Where do I generate a token? 

Optimizely Classic has a JavaScript API and a REST API available.

The Optimizely JavaScript (client) API provides a way for developers to modify the normal behavior of the Optimizely snippet for specific use cases. Use the API to target activation based on specific page content or events, query the state of activation, bucketing, or conversion for use in custom analytics packages, and force visitors into specific variations, among other capabilities.

The Optimizely REST API lets you create and manage Optimizely projects and the experiments inside of them. The API is RESTful and encodes data in JSON. The sections below explain how to authenticate with the API, form requests, and consume responses.

If you'd like to generate an API token, visit and view our documentation here.