Data files

namespace demo;

predicate lucky { "type": "minecraft:random_chance", "chance": 0.25 }

itemTag handles { "values": ["minecraft:stick", "minecraft:blaze_rod"] }

lootTable "minecraft:entities/zombie" {
  "type": "minecraft:entity",
  "pools": [{ "rolls": 1, "entries": [{ "type": "minecraft:item", "name": "minecraft:diamond" }] }]
}

mcfun tick() {
    if (predicate self:lucky) { /say lucky; }
}

Recipes, predicates, loot tables, advancements, tags and worldgen are JSON files in a pack, and a data file declaration writes one. The type word picks the folder and the name picks the file. The body is the JSON: an object, or a list for the few types that use one (blockTransformer). It is written unchanged, so you can paste output from a generator such as misode. A string id can replace a vanilla file, such as a loot table.

The example writes:

data/demo/predicate/lucky.json
data/demo/tags/item/handles.json
data/minecraft/loot_table/entities/zombie.json

The name is an identifier or a string:

Name	File	Id
lucky	data/demo/predicate/lucky.json (snake_case, like an mcfun)	demo:lucky, or self:lucky in commands
"checks/rare"	data/demo/predicate/checks/rare.json	none; type demo:checks/rare
"minecraft:entities/zombie"	data/minecraft/loot_table/entities/zombie.json	none; it replaces the vanilla file

In commands and conditions, refer to a data file by its name: if (predicate self:lucky) (see ids in commands). Inside JSON, write ids in full: "#demo:handles", or "demo:first_trident" for an mcfun firstTrident.

The type word is the folder name in camelCase. Worldgen types drop worldgen/, and a tag is the registry name followed by Tag:

Type words	Folder
advancement, recipe, predicate, lootTable, itemModifier, enchantment, damageType, dialog, jukeboxSong, trimMaterial, …	the same name in snake_case: loot_table, item_modifier, …
biome, feature, placedFeature, noiseSettings, densityFunction, structure, templatePool, …	worldgen/<name>
itemTag, blockTag, entityTypeTag, functionTag, biomeTag, …	tags/item, tags/block, tags/entity_type, tags/function, tags/worldgen/biome

The type words are only special at the top level of a file, so you can use recipe as a name inside an mcfun. A wrong word is an error with a suggestion: Unknown data file type 'recpie'. Did you mean 'recipe'?.

Costs and caveats

• The compiler only checks the JSON syntax. The game reads the contents when the pack loads, and a bad file can stop the world from loading: in 26.3, a predicate with "condition" in place of "type" gives No key type, and the server refuses to start.
• The body is plain JSON, so // and {{...}} aren’t read as Poplar.
• The minecraft:load and minecraft:tick function tags belong to Poplar. Use mcfun load and mcfun tick instead.