JSON-LD vs Microdata vs RDFa, which should Magento use?

JSON-LD. Google explicitly recommends it. Microdata still works but is deprecated for new implementations. RDFa is dead for ecommerce.

Why JSON-LD wins for Magento specifically:

• Decoupled from markup. Microdata interleaves itemprop attributes inside <div> trees, touch the layout, break the schema. JSON-LD lives in a single <script type="application/ld+json"> tag, isolated from the storefront DOM.
• Hyvä-safe. When you migrate Luma → Hyvä, your microdata-bound itemprop attributes are scattered across hundreds of phtml files. With JSON-LD you ship one block per page-type and the Hyvä migration leaves it alone.
• Faster for Google. JSON-LD parses faster than walking the DOM for microdata; Googlebot has an explicit fast-path for application/ld+json.
• Magento 2.4.7+ ships JSON-LD by default for Product. The core Magento_Catalog module emits it. Microdata is legacy.

This validator only validates JSON-LD. If you’re on microdata, your migration path is: extract microdata to a server-side template, emit it as JSON-LD via a Product block, then validate.