API or FUNCTION to add listing from an other app

Hi,

I’m using a custom built portal to manage the listings but I want to submit (via a POST json or custom) new listing or update existing listing (places or event).
Is there a API or PHP function I can call to do that.
I know I can just update the mysql data, but I rather use existing API/Function.
The new listing will only have : business name/address/phone, I need also a function to fetch the geodata.

NB: if there is existing API, a php sample script will be appreciated

Thanks