One of the first things you wish for when working with SharePoint 2013 REST api, is a way to display the raw data, so you know what you have to work with. The _api JSON Viewer app is the tool that does exactly that, with a very user-friendly display and simple functionality. It even allows you to view JSON data across the site collection and every apps. This is a must have app for anyone working with the SharePoint 2013 REST _api. This app is for viewing purpose only and do not make it possible to change data.