What's the perfect open source web API for code compilation and execution?

Long question - I want to integrate IDE(compiler) in my open source project. There will be source code input and simple output will be displayed. Which API should I use? (Condition - API should be open source or free)

I have been developing an open source project for managing code snippets(kind of github gists). But I want to add this functionality of providing online IDE for simple program execution.

I heard there are various online APIs from some of which are open source. But it is hard to find perfect one. So as people from community would have used API in past so I needed an opinion for integrating that as part of Easy-to-go routine.