itemGroup object

To put your fresh new item in a Creative Tab, you can define an itemGroup

By default if this parameter is not defined, your item is in the Misc/Material Creative Tab.

Example with vanilla creative tab

[
  {
    "registryName": "my_supa_item",
    "itemGroup" : "minecraft:redstone"
  }
]

Example with custom creative tab

[
  {
    "registryName": "my_supa_item",
    "itemGroup" : "super_pack:my_tab"
  }
]