Some kind of legal contract... Well, yes, it's called.. a contract. An API provider could put their obligations in writing, though they would probably have to

Some kind of legal contract... Well, yes, it's called.. a contract. An API provider could put their obligations in writing, though they would probably have to charge at least a small fee to make the contract stand. But providers are not going to do that unless developers make it worth their while, and vice-versa. The economics of open APIs just don't support that kind of commitment on either end. If you want to build a business around someone's free API, you better have a quick exit planned.