Open Graph is a protocol that allows developers to integrate their pages into the social graph. It was created by Facebook in 2010. The protocol uses meta tags in the HTML of a page to describe the content of the page. This allows Facebook to crawl and index the content of the page and display it in the Facebook news feed and other places on the site. The Open Graph protocol has been adopted by a number of other websites and services, including Twitter, LinkedIn, and Google+.
Facebook's Open Graph Debugger is a free service that allows developers to view how Facebook crawls and renders their pages. It also allows developers to see what data is being pulled from their pages by Facebook's Graph API.
Overall, the Facebook Open Graph Debugger is a helpful tool that can be used to ensure that your Facebook Open Graph tags are working correctly. This can be especially helpful if you're having trouble getting your Facebook Like button to work correctly.
The primary way for apps to read and write to the social graph. Access Pages, Users, Posts, Groups, Events and more.
[source: (https://developers.facebook.com/docs/apis-and-sdks/)]
The Marketing APIs offer programmatic access to manage your ad campaigns, Custom Audiences, and reports.
[source: (https://developers.facebook.com/docs/apis-and-sdks/)]