There’s no indicators per card in the game data that say if a card is craftable. But the rules are pretty simple if you wish to show some sort of indicator in an app. You can check the wiki for uncraftable cards (http://hearthstone.gamepedia.com/Uncraftable) and maybe create an array that holds the sets of uncraftable or craftable cards. Same goes for Standard and Wild. You could just create an array that holds the current Standard sets.

I’ll be looking into this ASAP.