Vary is а powerful HTTP header that plays a significant role in how your website cache is working. When this header is set correctly, it ensures that your site visitors see the right content, regardless of the caching applied. However, if this header is set up incorrectly, it can totally overrule even the benefits of the best caching system and cause resource overusage. In this blog post, I want to shed some light on how the Vary header affects your SiteGround hosted site and specifically our caching system, and to show you what’s the recommended use of Vary header for your site.