The Metrics API can be queried to retrieve metrics information for a day or a range of days. The current metrics it provides are usage (record views, types of views) and display_collection (statistics on display_collections, number of records in them, breakdown of copyright/categories).
To view the Swagger API documentation you can use the Swagger Editor, to load the Swagger API definition use
File -> Import URL... using
http://digitalnz.github.io/supplejack/assets/swagger.json as the URL.