Building for voice is more than writing a simple program and you're done. A good voice skill or action has many components that work together. Mark and Allen discuss what some of those components are, how they integrate, and what you should think about as you write them.  

Number Spies System Components: https://markvoicedev.medium.com/creating-an-alexa-game-number-spies-system-components-overview-41bf142d0b3c