Structured data is a standardized way of annotating webpage content so that search engines can interpret it programmatically. Instead of a crawler reading your page and guessing what a star rating or event date means, structured data labels those elements explicitly using a shared vocabulary.
The dominant vocabulary is Schema.org, a collaborative project backed by Google, Bing, Yahoo, and Yandex. It defines hundreds of entity types — from Article and Product to LocalBusiness and HowTo — each with its own set of properties.
Three syntax formats exist:
- JSON-LD — JavaScript Object Notation for Linked Data, injected in a
<script>tag. Google's recommended format and the easiest to maintain. - Microdata — HTML attributes added inline to existing markup. Older pattern; common in legacy CMS implementations.
- RDFa — Attribute-based like Microdata but more expressive. Used in some publishing and academic contexts.
What structured data is not: it is not a ranking factor in the direct sense. Google has confirmed it does not boost rankings because you added schema. What it does is make your content eligible for rich results — enhanced SERP features that can increase click-through rates when awarded.
It also feeds Knowledge Graph entries, voice search answers, and integrations with Google's AI-generated summaries. The use cases extend well beyond classic blue-link SEO.