anespa on "How to convert a plugin to API"

Dear friends,
I am using a wordpress application & a non-wordpress web site for an activity logging purpose . My need is , I have some plugins in my
wordpress APP that must be converted as a Common API , which can use by both for my wordpress app & web app . Do any one can advise how it can do?
I checked xmlrpc for same purpose . But don't get much idea .

I refer urls below
Convert API to Wordpress Plugin

Is it possible to extend Wordpress XMLRPC interface from a plugin?

Is there a wordpress plugin for creating an API from your site?

Please reply me with a solution asap

Thanks,
Anes