What is AggregateRating in Schema.org?

The stars that sometimes appear under a Google result, with "4.6" and the number of reviews next to them, come from something specific in the page's code: an AggregateRating node. It is a type from Schema.org. It is not a review: it is the average of all of them, with their count. Each individual review, with its author and its text, is another type, Review. It matters to you because it is the property in your structured data that is most visible when it works, and the one with the most rules about where the numbers can come from.

How it works

Schema.org defines AggregateRating as the average rating based on multiple ratings or reviews. It is a kind of rating (Rating) and, with the aggregateRating property, it can hang off a brand, a creative work, an event, an offer, an organization, a place, a service or a Product.⁠^{[1]Schema.org. AggregateRating} Its properties are few:⁠^{[1]Schema.org. AggregateRating}

Google uses it for the review snippet, which it describes as a short excerpt of a review or a rating, usually the average of many people's scores, and which can appear in rich results or in the knowledge panel with stars and other summary data.⁠^{[2]Google Search Central. Review snippet (Review, AggregateRating) structured data} For that it asks for:⁠^{[2]Google Search Central. Review snippet (Review, AggregateRating) structured data}

• ratingValue, the average, as a number, fraction or percentage.
• ratingCount or reviewCount, at least one of the two. Google spells out the difference: the first counts the ratings of the item on your site; the second, the people who left a review, with a score or without one.
• itemReviewed, what is being rated, unless the rating is nested inside another type with the aggregateRating property, which is the normal case on a product page: then it is omitted.
• The scale, if it is not the usual one. If bestRating is missing, Google assumes it is 5; if worstRating is missing, 1.

On a product, the rating is one of three doors to the product snippet: Google requires the name and at least one of these three properties, review, aggregateRating or offers.⁠^{[3]Google Search Central. Product snippet (Product, Review, Offer) structured data}

The rules matter as much as the properties. The ratings you mark up have to be visible to people visiting the page, and Google asks you not to gather reviews or ratings from other sites.⁠^{[2]Google Search Central. Review snippet (Review, AggregateRating) structured data} And there is an exception that surprises many businesses: if the rated entity controls the reviews about itself, its pages with local business or organization markup do not qualify for stars.⁠^{[2]Google Search Central. Review snippet (Review, AggregateRating) structured data} The rule is about that markup, the business's markup about itself; the ratings of the products it sells are marked up on the product.

In a store

A product page with its reviews and its node, side by side. Fictional example: the store, the product, the score and the number of reviews are made up.

{
  "@context": "https://schema.org",
  "@type": "Product",
  "name": "Coastal linen shirt, blue",
  "aggregateRating": {
    "@type": "AggregateRating",
    "ratingValue": "4.6",
    "reviewCount": "38"
  }
}

No itemReviewed, because it sits inside the product.⁠^{[2]Google Search Central. Review snippet (Review, AggregateRating) structured data} No bestRating, because the store's scale runs from 1 to 5, the one Google assumes.⁠^{[2]Google Search Central. Review snippet (Review, AggregateRating) structured data} And with the same numbers the customer sees: if the product page says 38 reviews, the node says 38, because structured data cannot mark up what the reader does not see.⁠^{[4]Google Search Central. General structured data guidelines} If the product page shows no reviews, the node carries no rating. Stores that publish with Clione follow that same rule: the rating on the product node comes from the store's own reviews (on BigCommerce, the platform's; on Shopify, the standard review metafields that the main apps write), and a product with no reviews carries none.

How to check

1. Search for aggregateRating in the source code of a product page and note ratingValue, ratingCount or reviewCount, and bestRating if there is one.
2. Compare them with what the customer sees at that moment: the same average and the same number of reviews, visible on the product page.⁠^{[2]Google Search Central. Review snippet (Review, AggregateRating) structured data}
3. Check the scale. If your ratings do not run from 1 to 5, the node has to say so with bestRating and worstRating.⁠^{[2]Google Search Central. Review snippet (Review, AggregateRating) structured data}
4. Confirm where the reviews come from: they have to be from your site, not gathered from others.⁠^{[2]Google Search Central. Review snippet (Review, AggregateRating) structured data}
5. Run the URL through the Rich Results Test to see what it detects and with which errors or warnings.⁠^{[5]Search Console Help. Rich Results Test}

Related concept: Review

AggregateRating and Review are often marked up together and answer different questions. Review is one specific opinion, with whoever wrote it and their score; AggregateRating is the average of many, with their count.⁠^{[1]Schema.org. AggregateRating} A product can carry both, and both types serve Google's review snippet, each with its own required properties.⁠^{[2]Google Search Central. Review snippet (Review, AggregateRating) structured data} If you want the stars to show with the number of reviews, the node that says it is AggregateRating; if you want to highlight what one customer wrote, it is Review. What your customers write, before it becomes markup, is product reviews, and they have an entry of their own.

To go further, the structured data reading path lays out the rest of the terms, and the Organization entry explains which markup describes the business and why it is not the place for its stars.