Minecraft Datapack Skill

Skill Scope

Routing Boundaries

• Use when: the deliverable is datapack files (pack.mcmeta, data/...) and .mcfunction/JSON content.
• Do not use when: the request is command-only snippets not tied to a datapack file tree (minecraft-commands-scripting).
• Do not use when: the request requires loader APIs, Java code, or runtime mod behavior (minecraft-modding).

---

Pack Metadata (1.21.x)

Minecraft Version	Preferred pack metadata
1.21 / 1.21.1	pack_format: 48
1.21.2 / 1.21.3	pack_format: 57
1.21.4	pack_format: 61
1.21.5	pack_format: 71
1.21.6	pack_format: 80
1.21.7 / 1.21.8	pack_format: 81
1.21.9 / 1.21.10	min_format: [88, 0], max_format: [88, 0]
1.21.11	min_format: [94, 1], max_format: [94, 1]

Use pack_format through 1.21.8. Starting in 1.21.9, Mojang replaced that
single field with explicit min_format / max_format values.
For exact patch targeting, use [major, minor] arrays for both min_format and
max_format, including .0 versions such as [88, 0]. A single integer is
equivalent to [major, 0] for min_format, while a single integer in
max_format allows any minor version on that major line. Do not write decimal
JSON numbers such as 94.1.

Keep pack.mcmeta exact for the patch you target instead of trying to span the
entire 1.21.x line with one metadata block.

---

Directory Layout

my-datapack/
├── pack.mcmeta
└── data/
    └── <namespace>/           ← use your pack's name (e.g., mypack)
        ├── function/
        │   ├── main.mcfunction
        │   └── tick.mcfunction
        ├── advancement/
        │   └── custom_advancement.json
        ├── recipe/
        │   └── custom_recipe.json
        ├── loot_table/
        │   └── custom_loot.json
        ├── predicate/
        │   └── is_night.json
        ├── item_modifier/
        │   └── add_name.json
        └── tags/
            ├── block/
            │   └── climbable.json
            ├── entity_type/
            │   └── bosses.json
            └── function/
                ├── load.json     ← runs on /reload
                └── tick.json     ← runs every game tick

---

pack.mcmeta

1.21.8 and earlier

{
  "pack": {
    "pack_format": 81,
    "description": "My Custom Datapack v1.0"
  }
}

1.21.9 / 1.21.10

{
  "pack": {
    "min_format": [88, 0],
    "max_format": [88, 0],
    "description": "My Custom Datapack v1.0"
  }
}

1.21.11

{
  "pack": {
    "min_format": [94, 1],
    "max_format": [94, 1],
    "description": "My Custom Datapack v1.0"
  }
}

---

Function Tags (load / tick)

data/<namespace>/tags/function/load.json

{
  "values": [
    "<namespace>:setup"
  ]
}

data/<namespace>/tags/function/tick.json

{
  "values": [
    "<namespace>:tick"
  ]
}

data/<namespace>/function/setup.mcfunction

# Runs once on /reload
scoreboard objectives add deaths deathCount
scoreboard objectives add kills playerKillCount
tellraw @a {"text":"[MyPack] Loaded!","color":"green"}

data/<namespace>/function/tick.mcfunction

# Runs every tick — KEEP THIS SHORT
# Only put fast, targeted operations here
execute as @a[scores={deaths=1..}] run function mypack:on_death_check

---

Commands and Function Syntax

Execute subcommands (datapack-specific patterns)

# Chained execute — common datapack pattern for conditional per-player logic
execute as @a[gamemode=!spectator] at @s if block ~ ~-1 ~ #minecraft:logs run give @s minecraft:apple

# store result into score (bridge between NBT world and scoreboard state)
execute store result score @s mypack.health run data get entity @s Health

# in: run logic in another dimension
execute in minecraft:the_nether run say This runs in the Nether

Storage NBT (datapack-specific global state)

# Storage is the datapack-native key-value store — persists across /reload
data modify storage mypack:data config.difficulty set value "hard"
data get storage mypack:data config.difficulty

# Copy live entity data into storage for macro use or cross-function state
data modify storage mypack:log last_player_pos set from entity @s Pos

For full command syntax, selectors, and scoreboard operations see the
Minecraft Wiki — Commands reference.
The minecraft-commands-scripting skill covers command-only work in depth.

---

Macros (1.20.2+)

Macro functions let you pass dynamic arguments to a function.

Define a macro function (data/mypack/function/greet.mcfunction)

# Macro argument: $(name)
$tellraw @a {"text":"Welcome $(name)!","color":"gold"}
$scoreboard players set $(name) points 0

Call with run function + with

# Pass values from storage
data modify storage mypack:tmp input set value {name:"Steve"}
function mypack:greet with storage mypack:tmp input

# Pass values from entity NBT
function mypack:greet with entity @p {}

# Pass value from block NBT
function mypack:greet with block 0 64 0 {}

---

Advancements

data/<namespace>/advancement/my_advancement.json

{
  "display": {
    "icon": {
      "id": "minecraft:diamond"
    },
    "title": {"text": "Diamond Hunter"},
    "description": {"text": "Mine your first diamond"},
    "frame": "task",
    "show_toast": true,
    "announce_to_chat": true,
    "hidden": false
  },
  "criteria": {
    "mined_diamond": {
      "trigger": "minecraft:item_picked_up",
      "conditions": {
        "item": {
          "items": ["minecraft:diamond"]
        }
      }
    }
  },
  "rewards": {
    "function": "mypack:on_diamond_obtained",
    "experience": 10
  }
}

Common advancement triggers

Trigger	When it fires
minecraft:impossible	Never (use for manual grants)
minecraft:tick	Every tick while player is online
minecraft:player_killed_entity	Player kills an entity
minecraft:entity_killed_player	Entity kills a player
minecraft:item_picked_up	Player picks up an item
minecraft:placed_block	Player places a block
minecraft:inventory_changed	Player inventory changes
minecraft:changed_dimension	Player changes dimension
minecraft:consume_item	Player consumes an item
minecraft:location	Player at a specific location
minecraft:recipe_unlocked	Player unlocks a recipe

---

Custom Recipes

Shaped crafting (data/<namespace>/recipe/shaped.json)

{
  "type": "minecraft:crafting_shaped",
  "pattern": [
    "DDD",
    "D D",
    "DDD"
  ],
  "key": {
    "D": { "item": "minecraft:diamond" }
  },
  "result": {
    "id": "minecraft:diamond_block",
    "count": 1
  }
}

Shapeless crafting

{
  "type": "minecraft:crafting_shapeless",
  "ingredients": [
    { "item": "minecraft:wheat" },
    { "item": "minecraft:wheat" },
    { "item": "minecraft:wheat" }
  ],
  "result": {
    "id": "minecraft:bread",
    "count": 2
  }
}

Smelting / blasting / smoking / campfire

{
  "type": "minecraft:smelting",
  "ingredient": { "item": "minecraft:beef" },
  "result": { "id": "minecraft:cooked_beef" },
  "experience": 0.35,
  "cookingtime": 200
}

Disable a vanilla recipe (override with empty file)

To remove a vanilla recipe, create a file at the same path under data/minecraft/recipe/
in your datapack with just {} as the content:

{}

For example, to disable the piston recipe, create:
data/minecraft/recipe/piston.json containing only {}.

Get the exact filename from the vanilla jar:
jar xf minecraft.jar data/minecraft/recipe/

Smithing transform

{
  "type": "minecraft:smithing_transform",
  "template": { "item": "minecraft:netherite_upgrade_smithing_template" },
  "base": { "item": "minecraft:diamond_sword" },
  "addition": { "item": "minecraft:netherite_ingot" },
  "result": { "id": "minecraft:netherite_sword" }
}

---

Loot Tables

data/<namespace>/loot_table/custom_chest.json

{
  "type": "minecraft:chest",
  "pools": [
    {
      "rolls": { "type": "minecraft:uniform", "min": 3, "max": 8 },
      "entries": [
        {
          "type": "minecraft:item",
          "name": "minecraft:diamond",
          "weight": 5,
          "functions": [
            {
              "function": "minecraft:set_count",
              "count": { "type": "minecraft:uniform", "min": 1, "max": 3 }
            }
          ]
        },
        {
          "type": "minecraft:item",
          "name": "minecraft:gold_ingot",
          "weight": 20
        },
        {
          "type": "minecraft:empty",
          "weight": 30
        }
      ]
    }
  ]
}

---

Predicates

data/<namespace>/predicate/is_daytime.json

{
  "condition": "minecraft:time_check",
  "value": { "min": 0, "max": 12000 }
}

data/<namespace>/predicate/player_has_diamond.json

{
  "condition": "minecraft:entity_properties",
  "entity": "this",
  "predicate": {
    "inventory": {
      "items": [
        { "items": ["minecraft:diamond"] }
      ]
    }
  }
}

Using predicates in functions

execute if predicate mypack:is_daytime run say It is daytime!
execute unless predicate mypack:player_has_diamond run tell @s You need a diamond!

---

Tags

Block tag (data/minecraft/tags/block/climbable.json — override vanilla)

{
  "replace": false,
  "values": [
    "minecraft:ladder",
    "minecraft:vine",
    "#minecraft:wool"
  ]
}

Item tag (data/<namespace>/tags/item/my_fuel.json)

{
  "replace": false,
  "values": [
    "minecraft:coal",
    "minecraft:charcoal",
    "minecraft:blaze_rod"
  ]
}

Use "replace": false to append to existing tags. Use "replace": true to completely
override (use with care for vanilla tags).

---

Worldgen Overrides

Override biome noise (data/minecraft/worldgen/noise_settings/overworld.json)

Edit inside an existing copy — do NOT create from scratch without the full JSON.
Get the vanilla version from the Minecraft jar: jar xf minecraft.jar data/.

Override a biome's spawn costs

{
  "spawn_costs": {
    "minecraft:zombie": {
      "energy_budget": 0.12,
      "charge": 0.7
    }
  }
}

---

Installation & Testing

# Place datapack in world folder
/datapacks/my-datapack/

# Or as a zip
/datapacks/my-datapack.zip

# In-game commands
/datapack list               # see all datapacks
/datapack enable "file/my-datapack"
/datapack disable "file/my-datapack"
/reload                      # hot-reload all datapacks without restart

Development workflow

1. Edit .mcfunction or .json files
2. Run the bundled validator to catch JSON and path errors before loading:

   ./scripts/validate-datapack.sh --root /path/to/datapack

3. If errors, fix and re-validate until clean
4. Run /reload in-game (or /minecraft:reload if a mod intercepts it)
5. Test with target command (e.g., /function mypack:setup, trigger an advancement)
6. Check latest.log for runtime errors (missing references, bad selectors)

---

Common Errors

Error	Cause	Fix
Unknown or invalid command	Syntax error in function	Check whitespace, selector, trailing space
Datapack did not load	Invalid JSON in any file	Validate with jq . < file.json
pack metadata mismatch	Wrong pack_format or min_format / max_format values	Update pack.mcmeta for the exact 1.21.x patch
Function not running on tick	Missing tick tag or wrong namespace	Check tags/function/tick.json path
Macro error	$ line but no with	Provide with storage/entity/block

Validator Script

Use the bundled validator script before shipping a datapack update:

# Run from the installed skill directory (for example `.codex/skills/minecraft-datapack`):
./scripts/validate-datapack.sh --root /path/to/datapack

# Strict mode treats warnings as failures:
./scripts/validate-datapack.sh --root /path/to/datapack --strict

What it checks:

• JSON validity for pack.mcmeta and data/**/*.json
• Legacy pluralized path mistakes for loot tables, functions, and block/item/function tags
• tags/function/load.json and tags/function/tick.json references resolve to real .mcfunction files

---

References

• Minecraft Wiki — Data Pack: https://minecraft.wiki/w/Data_pack
• Minecraft Wiki — Function: https://minecraft.wiki/w/Function_(Java_Edition)
• Minecraft Wiki — Commands: https://minecraft.wiki/w/Commands
• Pack format history: https://minecraft.wiki/w/Pack_format
• NBT format: https://minecraft.wiki/w/NBT_format
• Predicate conditions: https://minecraft.wiki/w/Predicate
• Loot table format: https://minecraft.wiki/w/Loot_table