I'm not sure if this is supposed to be USA-only or not. It seems to ask for 'country', so I assume it's aimed at the whole world. And here's where reality disagrees with your simple organisation. * First "zip code" is mostly an American term, "post code" is used in other anglosphere countries. * Not all countries have "everyone is in a city" model, this seems to happen in the USA, where 'city' is often an administrat…
So if I try http://zip.elevenbasetwo.com/?zip=1010
It gives: {"country": "US", "state": "MA", "city": "BRIMFIELD"}