I'm leery of building anything on top of someone else's API. I built on top of an API while also keeping in active contact with the company to let them know wh

I'm leery of building anything on top of someone else's API. I built on top of an API while also keeping in active contact with the company to let them know what I was doing, going as far as talking directly to their legal department, and they still shut me down when they couldn't handle the volume of usage. And this is in a situation where every marginal use of their API made them money. Collectively I was going to make them revenue of (projected admittedly) $1.2M. Didn't stop them from shutting me down. Long story short: Building on someone else's API is a recipe for disaster. Are there times when you have to? Sure. But you need to know what you are getting into.