NBTHelpers

Lets scripts distinguish numbers, lists, and compounds in NBT data through the NBTHelpers global.
List includes array-tag helpers; string tags have no separate helper class.

const player = Player.getPlayer();  
if (player !== null) {
  const tag = player.getNBT();  
  if (tag instanceof NBTHelpers.Compound) {
    Chat.log(tag.getKeys());  
  }
}

These names are available in JavaScript and Python without importing anything. They are read-only aliases of Java types, so instanceof works as usual.

Script name	What it is
NBTHelpers.Compound	Wraps a compound tag and provides access to its keys and values.
NBTHelpers.Element	Wraps an NBT tag and provides type checks, typed helper views, and path lookup.
NBTHelpers.List	Provides indexed access to list and array tags, and converts four-int arrays to UUIDs.
NBTHelpers.Number	Wraps a numeric tag and provides conversions to primitive numeric types.