The HTML Encryption tool from SiteAnalyzer, available under their Online SEO Tools section, allows users to encrypt HTML code by converting it into JavaScript code. Users can paste their HTML code into the tool, which then outputs the encrypted version to help protect the original HTML content. This feature is useful for web developers and SEO specialists aiming to safeguard their sites code from direct copying or alteration. The tool is part of a broader suite of popular SEO utilities provided by SiteAnalyzer, enhancing website security and optimization efforts.