Build Big is running a plugin called AutomaticInventory.

AutomaticInventory simplifies inventory management tasks:

  • /DepositAll finds nearby chests and instantly deposits items from your inventory matching the items in each chest! (Doesn't disturb hotbar or shield hand).
  • Automatically sorts personal inventory and chest contents.
  • Automatically replaces both broken tools and depleted hot bar stacks.

Some players dislike the automatic sorting feature. You can disable automatic sorting for your inventory by doing /autosort inventory and automatic sorting for your chests by doing /autosort chest (both commands work as a toggle.)