Someone pointed out to me this command: StringToBase64
But does AppGameKit not have a command to decode the base64 back?

I have my own code for encoding/decoding base64, a new user has pointed out some efficiency improvements to it. The internal command to encode is way faster, so if there's a function to decode that's not documented that could really improve things.

No, there isn't. I had to write one when I did my own XML and TMX functions. Would be a good feature request.

integer Val( str, base )
base - The base that the string number is in.