Short answer—no, it won't. Smartlook’s tracking script loads asynchronously, meaning it doesn’t prevent the rest of your website from loading while it downloads, and the load time of our script is negligible on most websites.
That being said, every website is different, so measuring speed on different websites may show differing results. Also, page speed measuring tools don’t always paint an accurate picture when analyzing scripts like Smartlook. You can often see the same issues with the Google Analytics script, and the warnings you see in various page speed tools doesn’t mean that the Smartlook script will slow down your website.
Since all the data flows between the Smartlook script and our server, your server will never be burdened with any extra data. We take site performance very seriously and constantly optimize the Smartlook script to improve load time, and use various tools and services like CDNs (content delivery networks) to load our script as fast as possible everywhere around the globe.