Website OS Checker tool checks what operating system a website/domain is using on their backend server. It helps to analyze the technology used by a specific website. Some websites like to adapt to every latest OS release, but some do not pay attention to the upgradation and continue to use the old technology or old versions of specified operating systems. It is better to use the latest OS versions to avoid attacks and vulnerabilities and to make the security of a website tight. If a website is behind a front-end cloud proxy services like Cloudflare or Sucuri, then it's likely for you to see the OS of Cloudflare server instead of the website's original server because we cannot check the hidden IP of a site and we can only check the public data provided by a website.