What schema markup is, how it is written, and what Google does with it

HTML tells a browser how to display text, not what the text means. Schema.org's own example is a heading that reads Avatar, which could be the film or a profile picture. Schema markup closes that gap. It labels parts of a page with types and properties from the schema.org vocabulary, so a search engine can tell that a page is about a particular movie, person, place or recipe.

Schema.org says its vocabulary is understood by Google, Microsoft, Yandex and Yahoo. Google calls the result structured data: a standardized format for giving information about a page and classifying its content.

The vocabulary can be written in three formats: JSON-LD, Microdata and RDFa. JSON-LD sits in a script block in the page, and Google's recipe example uses it to describe the recipe name, author, publish date and cooking times.

Microdata, introduced with HTML5, puts the labels on the visible HTML itself. The itemscope attribute marks the block that is about one item, itemtype says what kind of item it is, and itemprop labels each property, such as a movie's name, director or genre. A property's value can be another item with its own properties, such as a director who is a Person with a name and a birth date.

Google says it uses structured data to understand a page's content and to gather information about the web and the world, such as the people, books or companies in the markup. On a recipe page, the labels can let Google show a rich result and let people find the recipe by ingredient, calories or cooking time.

Google publishes case studies. Rotten Tomatoes saw a 25% higher click-through rate on pages with structured data across 100,000 pages. Food Network saw 35% more visits after converting 80% of its pages. Rakuten found visitors spent 1.5 times longer on pages with structured data. These are results reported by the companies, not promises for any other site.

Google's main rule is that markup must describe the page it sits on. Don't build empty pages just to hold structured data, and don't mark up information that visitors can't see, even if it is true. Google's general structured data guidelines carry the fuller technical and quality rules.

Sites on a CMS such as Wix, WordPress or Shopify may not be able to edit HTML directly. Google suggests looking for a search engine settings page or a plugin that adds structured data. Whatever writes the markup, check it with the Rich Results Test before relying on it.