Getting started

A friendly, correct-from-the-first-line walkthrough: build your first Minecraft Java data pack for 1.21+, wire a function to run on load and every tick, reload it in-game, and troubleshoot when nothing happens.

What you'll build

A tiny data pack called my_pack that prints a message once when the world loads and quietly counts every game tick. By the end you'll understand the four moving parts every pack shares: the pack.mcmeta file, a namespace, a .mcfunction, and the #minecraft:load / #minecraft:tick function tags.

Step 1 — Create the folder

In your world's save directory, open the datapacks/ folder and make a new folder for your pack. On a typical singleplayer install:

.minecraft/saves/<your world>/datapacks/my_pack/

Everything else lives inside my_pack/. You can also add the pack during world creation on the "More" → "Data Packs" screen, but dropping the folder into an existing world's datapacks/ is the fastest way to iterate.

Step 2 — Write pack.mcmeta

Every pack needs exactly one file at its root: pack.mcmeta. It's a small JSON file that tells Minecraft which format your pack is written for and what to show on hover.

my_pack/pack.mcmeta

{
  "pack": {
    "pack_format": 48,
    "description": "My first data pack"
  }
}

"pack_format": 48 is the value for 1.21. The description is the text shown when you hover the pack in the list — set it to something, even trivial, so it doesn't look broken.

Step 3 — Make a namespace

All of a pack's content lives under data/<namespace>/. A namespace is your project's unique prefix; use a lowercase, snake_case name that won't collide with other packs. We'll use my_pack:

my_pack/
├── pack.mcmeta
└── data/
    └── my_pack/          # <- your namespace
        └── function/     # .mcfunction files go here (singular folder!)

Files you place here get an ID of the form namespace:path. So data/my_pack/function/hello.mcfunction becomes the function my_pack:hello. Valid namespace/path characters are a-z 0-9 _ - . (and / in the path only).

Step 4 — Write your first function

A function is a plain-text .mcfunction file: one command per line, run top to bottom. Create two of them — a setup message and a tick counter.

data/my_pack/function/hello.mcfunction

# Runs once when the pack loads
say My first data pack is loaded!
scoreboard objectives add my_pack.ticks dummy

data/my_pack/function/loop.mcfunction

# Runs every tick — keep tick work light!
scoreboard players add #timer my_pack.ticks 1

Lines starting with # are comments. The hello function creates a scoreboard objective; the loop function bumps a fake player counter once per tick.

Step 5 — Hook it to load & tick

Minecraft runs your functions automatically when they're listed in two special vanilla function tags: #minecraft:load (once on world load and after every /reload) and #minecraft:tick (every tick, 20 times a second). These tag files live under the minecraft namespace:

my_pack/
└── data/
    ├── my_pack/
    │   └── function/
    │       ├── hello.mcfunction
    │       └── loop.mcfunction
    └── minecraft/
        └── tags/
            └── function/
                ├── load.json
                └── tick.json

data/minecraft/tags/function/load.json

{
  "values": [ "my_pack:hello" ]
}

data/minecraft/tags/function/tick.json

{
  "values": [ "my_pack:loop" ]
}

These are ordinary tags, so if another pack also adds to #minecraft:load, both packs' entries are kept (tags merge). See Tags for the full merge/replace rules.

Step 6 — Reload & test

With the pack in place, load the world and run:

/reload

/reload re-reads your functions, tags, recipes, loot tables, and more without leaving the world, then fires #minecraft:load. You should see the say message appear immediately. To run a function by hand:

/function my_pack:hello

Confirm the pack is enabled and check its load order any time with:

/datapack list
/datapack list enabled

Troubleshooting

If /reload runs but nothing happens, work down this list — the causes are almost always structural, not logical.

Next steps

• Pack structure & pack.mcmeta — the full folder tree, every registry folder, namespaces, overlays, and the complete pack.mcmeta schema.
• Functions — commands, macros, scheduling, and structuring larger packs.
• Tags — how #minecraft:load, #minecraft:tick, and other tags merge and order.

Sources

• Tutorial: Creating a data pack — Minecraft Wiki
• Data pack — Minecraft Wiki
• pack.mcmeta — Minecraft Wiki
• /datapack command — Minecraft Wiki