Use a tag manager with Optimizely Web Experimentation

You should not use a tag manager to load Optimizely's snippet. Loading Optimizely through a tag manager can cause issues such as page flashing, where the original version of your page is briefly displayed to visitors before the Optimizely experiment. It can also cause issues with your analytics integrations.

To deliver the best experience to your visitors, you should implement Optimizely outside of a tag manager.

If you must use a tag manager to load Optimizely, the following sections describe potential pitfalls. Contact your Customer Success Manager to discuss implications for your site.

Load Optimizely synchronously

To ensure that Optimizely loads and integrates correctly, ensure that Optimizely can finish loading before other tags on your page execute. This is called synchronous loading because all tags load one after the other. To ensure synchronous loading:

Load Optimizely Web Experimentation in the tag of your page, outside of a tag manager(recommended, especially with Google Tag Manager).
Use a tag manager that supports synchronous loading such as Tealium or Ensighten (not Google Tag Manager).

Potential pitfalls and best practices

Here are some potential pitfalls to loading Optimizely through a tag manager that does not support synchronous loading, especially Google Tag Manager:

If you partially deploy Optimizely on your site, you may not deploy Optimizely on some pages where you want to track goals or events. This will cause goals or events not to track.
Another person in your organization unfamiliar with Optimizely may change your configuration and cause side effects.
If you load Optimizely asynchronously, your analytics integrations may not function properly and you could see a "flicker" or "flash" effect, where the original page shows briefly before the variation loads.

Loading Optimizely Web Experimentation outside your tag manager can help avoid these issues.

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Note
You can use your tag manager to deploy data layer events in Optimizely that you might normally place on your page, like custom event goals.

If you load Optimizely and a tag manager on your site, load Optimizely outside your tag manager (especially if you use Google Tag Manager).

Place the Optimizely snippet at the top of the tag of your site, then place your tag manager below the Optimizely snippet, just like you would normally place your analytics tags below Optimizely code.
```
<head>
   <script type="text/javascript" src="//cdn.optimizely.com/js/12345678.js"></script>
</head>
<body>
   // Insert Tag Manager Code Here
</body>
```

Use a tag manager with Optimizely snippet

Load Optimizely synchronously

Potential pitfalls and best practices

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Load Optimizely synchronously

Potential pitfalls and best practices

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