Traditional web technologies like HTML and CSS focus primarily on formatting content to make it more understandable. Semantic web technologies like RDFa, Microdata, and JSON-LD extend the traditional web in ways that make it easier for machines (primarily search engines) to understand. While it is relatively simple to determine if a page looks as it is intended to, determining if the structured data it contains is properly formatted can be more difficult. Google's Structured Data Testing Tool provides a way to validate the semantic web information exposed on a page. It shows users which elements Google actually understood and what went wrong with the ones that weren't understood. By following the "Learn more about this tool" link, users can find an introduction to semantic web and structured data concepts along with detailed reference material. The Structured Data Testing Tool works in any modern browser.