This mod adds commands /dupe and /dupefast and their customization gamerules.
/dupe to dupe any item in main-hand. If amount of items in main-hand * 2 >=MaxItemstack it becomes MaxItemstack.
/dupefast to create a maximum amount of items in a main-hand(can be changed with /gamerule MaxItemstack <number>)
All gamerules:
/gamerule IsDupeEnabled true/false - are dupe commands executable on this server(True by default).
/gamerule dupePermissions 0/1/2 - 0 - anyone can execute dupe commands, 1 - only players in creative mode can execute dupe commands, 2 - only admins of the server(command permissions 4) can execute dupe commands(0 by default).
/gamerule allowStackedItemsDupe - switches between giving you items and setting them in main-hand so stacked items cant/can be stacked(True by default)
/gamerule maxItemstack <any number> - sets the maximum number of items that can be in a hand to be duped(64 by default)