How to check if Xbox Live Gold Code is good on my iPhone?

I know there's an app but i don't know what it's called gonna buy a gold card today from some guy and I wanna know if it's good or not don't wanna get scammed by this guy and it ends up he gave me a stolen non-activated card you know? Does anyone know an app that does this I have that Xbox smart glass but it doesn't do anything it sucks

You can get certain apps. Just go to the app store and look up xbox live

XBOX Live Codes Generator v4 http://ultrahacks.net/xbox-live-codes-generator-v4/