Structured data is a promise about the page it sits on. A JSON-LD block that says your app costs 12 USD, that support is at a certain address and that you're the same company as a given GitHub account is a set of claims. Search engines and AI assistants can only use those claims safely if the page backs them up.

Google is explicit about this. Its general structured data guidelines say: "Don't mark up content that is not visible to readers of the page. For example, if the JSON-LD markup describes a performer, the HTML body must describe that same performer." The same page adds that "your structured data must be a true representation of the page content."

Most validators don't check that part. They check syntax and required properties.…