JSON-LD
A format for embedding structured data as a block of JSON directly inside a webpage's code.
What is JSON-LD?
JSON-LD (JavaScript Object Notation for Linked Data) is a way of writing structured data as a plain block of JSON (a simple, widely-used data format) and embedding it directly in a webpage's HTML. It lets a page state facts explicitly, like "this page describes a Product named X with price Y," in a format a program can parse instantly without touching the visible page layout at all.
Why it matters
JSON-LD 1.0 reached W3C Recommendation status on January 16, 2014, with JSON-LD 1.1 following as a full W3C Recommendation in 2020, adding features like framing and better support for expressing relationships between linked data documents. On the web it's most commonly inserted as a script type="application/ld+json" element in a page's HTML (invisible to visitors but fully visible to crawlers) which is why Google Search Central recommends it as the preferred format for structured data over the older alternatives, Microdata and RDFa, both of which require tagging the visible HTML itself. Because the JSON-LD block is self-contained, it can describe entities and relationships, such as a Product's variants or a Review's author, that don't map cleanly onto the visible page markup at all.