Rich Snippets are very popular markup elements added to existing content to make it easier for search engines to determine the use of the content or enhance the scanned content for the search results page. And, the very first rich snippets added by Google years ago is related to ratings, and Google can show rating stars along with the search results for selected content.
But, over the years, the rich snippets have evolved to the point of being very, very convoluted, with Google making changes to the snippets rules each year, making it very hard for the website owners to have fully compliant snippets that will be used by Google in search results. GD Rating System Pro has a Rich Snippets Addon attempts to make this process easier, by implementing compliant rich snippets support that will include ratings as reviews or aggregated ratings (or both).
The plugin implements various snippet types, and in global settings, you can choose rating type for each post type. You can also choose the method for displaying snippets: JSON-LD (prefered method) or Microdata. And, for each post type, you can choose the rating and review methods to pull the rating data from for individual posts.
Individual Posts Settings
But, for most snippet types, you need to provide additional information for each post that uses it. The plugin can generate a lot of snippet required data, but in some cases, for some snippet types, there is simply no way to do it automatically, and that is why each post shows metabox for rich snippets, where you can override global snippet settings, and configure additional parameters for the selected snippet mode/type.
Search Engine Compatibility
The goal is to provide snippets that are valid, but there is no way to force Google or other search engines to use rich snippets from every website. With all the changes Google makes every few months in relation to snippets, we will try to update the user guide related to rich snippets in GD Rating System Pro and make changes to the plugin to make it better and more up to code of what Google requires.