Definition

Schema markup is machine-readable data embedded in a page, usually as JSON-LD, that states what the page is about in a fixed vocabulary: an organisation, a product, a price, an author, a date. It does not change what a human sees.

Why it matters

It removes guesswork about facts that are easy to get wrong by reading prose, such as which of several names is the company and what the price actually applies to. Ambiguity is what produces confidently wrong AI answers about a brand.

How to measure it

Extract the JSON-LD a page actually serves and check it validates and matches the visible content. Markup that describes something the page does not show is worse than none.