For over 7 months the custom recipe feature is missing the ability to parse more data like nbt. This was shown by MC-122622, but it was closed for beeing "Invalid" after beeing confirmed to be added. But after digging a bit and trying some stuff I'm sure that Minecraft should be able to support it, but the parser just ignores the nbt data. The network packets based on http://wiki.vg/Pre-release_protocol#Declare_Recipes send Itemstacks that can contain nbt, and in the 1.13-pre1 in the class au.class the method "public static au a(@Nullable JsonElement ?)" is the correct parser to load the ItemStack with the nbt. The recipe parser seems to be using azb.class "public static awr a(JsonObject ?)" which only loads the itemtype and amount. For some reason booth check for a "data" tag and throw an error "Disallowed data tag found", even when it doesn't do anything. The wiki lists https://minecraft.gamepedia.com/Recipe the "tag" tag as supported in recipes for 1.13, but it isn't implemented right now. Nbt tags should be added to the input and output items of recipes.