Everyone should be aware that Google just made many changes to their apis. some of them were deprecated.
The Google API is obtained form Google, on the left of that a.m. Google API-FAQ page you find the link to create account ( @ google ) .. then you get your google API
Most APIs are little more than naked features - and there's a big gap between a feature and a service. Understand what you need to do to CYA (cover your API)."The only reason you'd have only a SOAP API is because you hate 80% of your addressable market." - @sramji There's usually little argument that a REST API is easier to use than a SOAP API. But how important is it to be 'truly' or 'strictly' RESTful? That is, adhering to standard HTTP operations or 'verbs' - GET, PUT, DELETE, POST - on well defined resources, as opposed to the common practice of embedding 'verbs' or operations as methods in a GET URL. Typically, security is cited as the big advantage of 'true REST' (with some good discussions here and here). However, a truly RESTful API may help you boost developer adoption. For example, imagine a 'shopping cart'
To my Knowledge, the api kep has been replaced by the SOAP API key, which has different functions and may not work the same.