are a set of defined HTML classes created to serve as consistent and descriptive metadata about an element, designating it as representing a certain type of data (such as contact informationgeographic coordinates, events, blog posts, products, recipes, etc.).

Designed to pair with RSS for automatically pulling info from web resources

  • these seem to be used to populate data for search engine cards too like recipes, shop items, etc.

in 2023, seems to have been replaced mostly by JSON-LD (Google uses them for “Rich Snippets”)


  • no new formats since 2005 (not flexible to change?)
  • accessibility concerns because uses elements that screenreaders dont take into account from
  • issue is that it overloads CSS classes and is just plain ugly and not very developer friendly
    • a lot of this could be helped by a comprehensive type system that is integrated into editors but you don’t get that in html..