Hey! Marc MacLeod here - founder. Basically, you put Prism between your API consumer (mobile app, website, integration tests, library, curl request, whatever) and the API itself.

Prism processes the traffic that passes through it, and generates your spec code from that. It can identify dynamic parameters in the url, build json schemas, etc.

Here's a little post + video we put together: https://medium.com/oh-what-a-wonderful-web/how-to-generate-2...

And another, demonstrating a slightly different process of generating spec code from the Peach mobile app API traffic:

http://peach.api-docs.io/1.0/welcome