Longer Query

{
  allSitePlugin {
    totalCount
    edges {
      node {
        name
        version
        packageJson {
          description
        }
      }
    }
  }
}

Gatsby structures its content as collections of nodes, which are connected to each other with edges. In this query you ask for the total count of plugins in this Gatsby site, along with specific information about each one.

Try using the editor's autocomplete (Ctrl + Space) to get extended details from the packageJson nodes.