minecraft-datapack-language 10.1.21

Compile JavaScript-style MDL language or Python API into a Minecraft datapack (1.21+ ready). Features variables, control flow, error handling, and VS Code extension.

Minecraft Datapack Language (MDL) v10

A powerful compiler that lets you write Minecraft datapacks in a modern JavaScript-style language (.mdl) or via a clean Python API, and then compiles to the correct 1.21+ datapack folder layout automatically.

📖 View Full Documentation - Complete guides, examples, and API reference
📦 View on PyPI - Download and install from PyPI
🔧 VS Code Extension - Syntax highlighting, IntelliSense, and snippets

🆕 Version 10 - JavaScript-Style MDL Language

Version 10 introduces a completely new JavaScript-style MDL language format with modern programming features:

✨ New Features in v10

• 🎯 JavaScript-style syntax with curly braces {} and semicolons ;
• 📝 Modern comments using // and /* */
• 🔢 Variable system with num, str, and list types
• 🔄 Advanced control flow including switch, try-catch, break, continue
• 📦 Import system for modular code organization
• 🎨 VS Code extension with full IntelliSense and snippets
• 🧪 Comprehensive testing with E2E validation
• 📚 Extensive documentation with examples for every feature

🔄 Migration from v9

• Version 9 and below used a different MDL format with indentation-based blocks
• Legacy documentation is available for users still using the old format
• Automatic migration tools are provided for converting old projects

🏗️ Core Features

• ✅ Handles the directory renames from snapshots 24w19a (tag subfolders) and 24w21a (core registry folders)
• ✅ Easy hooks into minecraft:tick and minecraft:load via function tags
• ✅ Creates tags for function, item, block, entity_type, fluid, and game_event
• ✅ Unlimited nesting support for complex control flow structures
• ✅ Multi-file projects with automatic merging and dependency resolution
• ✅ Error handling with try-catch blocks and custom error messages
• ✅ Type system with number, string, and list variables
• ✅ Function system with parameters, return values, and recursion

Note: Version 10 uses pack_format 82 by default for the new JavaScript-style syntax. Legacy projects can still use pack_format 48.

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🚀 Install

Option A — from PyPI (recommended for users)

Global, isolated CLI via pipx:

python3 -m pip install --user pipx
python3 -m pipx ensurepath    # reopen terminal
pipx install minecraft-datapack-language

mdl --help

Virtualenv (if you prefer):

python3 -m venv .venv
source .venv/bin/activate      # Windows: .\.venv\Scripts\Activate.ps1
pip install minecraft-datapack-language

Option B — from source (for contributors)

# inside the repo
python -m pip install -e .

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🔄 Update

• pipx: pipx upgrade minecraft-datapack-language
• pip (venv): pip install -U minecraft-datapack-language
• Pin a version: pipx install "minecraft-datapack-language==10.0.0"

---

💻 CLI

New JavaScript-style MDL (v10)

# Create a new v10 project
mdl new my_pack --name "My Pack" --pack-format 82

# Build JavaScript-style MDL files
mdl build --mdl my_pack/mypack.mdl -o dist --wrapper mypack
mdl check my_pack/mypack.mdl

# Multi-file projects
mdl build --mdl my_pack/ -o dist      # Build entire directory
mdl build --mdl "file1.mdl file2.mdl" -o dist  # Build specific files

Legacy MDL (v9 and below)

# For legacy projects, use pack-format 48
mdl build --mdl legacy_pack.mdl -o dist --pack-format 48

Build a whole folder of .mdl files

mdl build --mdl src/ -o dist
# Recursively parses src/**/*.mdl, merges into one pack (errors on duplicate functions).
# Only the first file should have a pack declaration - all others are modules.

Build multiple specific .mdl files

mdl build --mdl "src/core.mdl src/features.mdl src/ui.mdl" -o dist
# Parses multiple specific files and merges them into one datapack.
# Only the first file should have a pack declaration - all others are modules.

Validate a folder (JSON diagnostics)

mdl check --json src/

---

📝 Quick Start - JavaScript-style MDL (v10)

Create your first JavaScript-style MDL project:

// my_pack.mdl
pack "My First Pack" description "A simple example" pack_format 82;

namespace "example";

// Global variables
var num counter = 0;
var str message = "Hello World";

function "init" {
    say Initializing...;
    counter = 0;
    message = "Ready!";
}

function "tick" {
    counter = counter + 1;
    
    if "score @s counter matches 10" {
        say Counter reached 10!;
        counter = 0;
    }
    
    for player in @a {
        effect give @s minecraft:speed 1 0;
    }
}

// Lifecycle hooks
on_load "example:init";
on_tick "example:tick";

Build and test:

mdl build --mdl my_pack.mdl -o dist
# → dist/my_pack/... and dist/my_pack.zip

---

📁 Multi-file Support

MDL supports building datapacks from multiple .mdl files. This is useful for organizing large projects into logical modules.

How it works

• Directory scanning: When you pass a directory to --mdl, MDL recursively finds all .mdl files
• File merging: Each file is parsed into a Pack object, then merged into a single datapack
• Conflict resolution: Duplicate function names within the same namespace will cause an error
• Pack metadata: Only the first file should have a pack declaration (name, description, format)
• Module files: Subsequent files should not have pack declarations - they are treated as modules
• Single file compilation: When compiling a single file, it must have a pack declaration

Best practices

• One pack declaration per project: Only the first file should have a pack declaration
• Module files: All other files should not have pack declarations - they are treated as modules
• Single file requirement: When compiling a single file, it must have a pack declaration
• Organize by namespace: Consider splitting files by namespace or feature
• Use descriptive filenames: core.mdl, combat.mdl, ui.mdl etc.
• Avoid conflicts: Ensure function names are unique within each namespace

Example project structure

my_datapack/
├── core.mdl          # ✅ HAS pack declaration
├── combat/
│   ├── weapons.mdl   # ❌ NO pack declaration (module)
│   └── armor.mdl     # ❌ NO pack declaration (module)
├── ui/
│   └── hud.mdl       # ❌ NO pack declaration (module)
└── data/
    └── recipes.mdl   # ❌ NO pack declaration (module)

Important: Only core.mdl should have a pack "Name" declaration. All other files are modules that merge into the main pack.

Usage Examples

Build from directory:

mdl build --mdl my_datapack/ -o dist

Build from specific files:

mdl build --mdl "core.mdl combat.mdl ui.mdl" -o dist

Check entire project:

mdl check my_datapack/

Check with verbose output:

mdl build --mdl my_datapack/ -o dist --verbose

Complete Multi-File Example

Here's a complete example showing how to organize a datapack across multiple files:

core.mdl (main file with pack declaration):

// core.mdl - Main pack and core systems
pack "Adventure Pack" description "Multi-file example datapack" pack_format 82 min_format [82, 0] max_format [82, 1] min_engine_version "1.21.4";

namespace "core";

function "init" {
    say [core:init] Initializing Adventure Pack...;
    tellraw @a {"text":"Adventure Pack loaded!","color":"green"};
}

function "tick" {
    say [core:tick] Core systems running...;
    execute as @a run particle minecraft:end_rod ~ ~ ~ 0.1 0.1 0.1 0.01 1;
}

// Hook into vanilla lifecycle
on_load "core:init";
on_tick "core:tick";

combat/weapons.mdl (combat module):

// combat/weapons.mdl - Weapon-related functions
namespace "combat";

function "weapon_effects" {
    say [combat:weapon_effects] Applying weapon effects...;
    execute as @a[nbt={SelectedItem:{id:'minecraft:diamond_sword'}}] run effect give @s minecraft:strength 1 0 true;
}

function "update_combat" {
    function core:tick;
    function combat:weapon_effects;
}

combat/armor.mdl (armor module):

// combat/armor.mdl - Armor-related functions
namespace "combat";

function "armor_bonus" {
    say [combat:armor_bonus] Checking armor bonuses...;
    execute as @a[nbt={Inventory:[{Slot:103b,id:"minecraft:diamond_helmet"}]}] run effect give @s minecraft:resistance 1 0 true;
}

function "update_armor" {
    function combat:armor_bonus;
}

ui/hud.mdl (UI module):

// ui/hud.mdl - User interface functions
namespace "ui";

function "show_hud" {
    say [ui:show_hud] Updating HUD...;
    title @a actionbar {"text":"Adventure Pack Active","color":"gold"};
}

function "update_ui" {
    function ui:show_hud;
    function combat:update_combat;
    function combat:update_armor;
}

data/recipes.mdl (data module):

// data/recipes.mdl - Custom recipes
namespace "data";

// Custom recipe for a special item
recipe "special_sword" {
    {
        "type": "minecraft:crafting",
        "pattern": [
            " D ",
            " D ",
            " S "
        ],
        "key": {
            "D": {"item": "minecraft:diamond"},
            "S": {"item": "minecraft:stick"}
        },
        "result": {
            "item": "minecraft:diamond_sword",
            "count": 1
        }
    }
}

// Function tag to run UI updates
tag function "minecraft:tick" {
    add "ui:update_ui";
}

Project structure:

adventure_pack/
├── core.mdl              # ✅ HAS pack declaration
├── combat/
│   ├── weapons.mdl       # ❌ NO pack declaration (module)
│   └── armor.mdl         # ❌ NO pack declaration (module)
├── ui/
│   └── hud.mdl           # ❌ NO pack declaration (module)
└── data/
    └── recipes.mdl       # ❌ NO pack declaration (module)

Build the project:

mdl build --mdl adventure_pack/ -o dist --verbose

This will create a datapack with:

• Core systems (initialization and tick functions)
• Combat features (weapon and armor effects)
• UI elements (HUD display)
• Custom data (recipes and tags)
• Cross-module calls (UI calls combat functions)

CLI Options for Multi-file Builds

• --mdl <path>: Path to .mdl file, directory, or space-separated file list
• --src <path>: Alias for --mdl (same functionality)
• -o, --out <dir>: Output directory for the built datapack
• --wrapper <name>: Custom wrapper folder/zip name (default: first namespace or pack name slug)
• --pack-format <N>: Minecraft pack format (default: 48 for 1.21+)
• -v, --verbose: Show detailed processing information including file merging
• --py-module <path>: Alternative: build from Python module with create_pack() function

Error Handling

• Missing pack declaration: Single files must have a pack declaration
• Duplicate pack declarations: Only the first file in a multi-file project should have a pack declaration
• Function conflicts: Duplicate function names within the same namespace will cause an error
• Clear error messages: Errors include file paths and line numbers for easy debugging

---

📝 The .mdl language

Grammar you can rely on (based on the parser)

• pack header (required once):

  pack "Name" [description "Desc"] [pack_format N] [min_format [major, minor]] [max_format [major, minor]] [min_engine_version "version"];
  

• namespace (selects a namespace for following blocks):

  namespace "example";
  

• function (curly braces + semicolons):

  function "hello" {
      say hi;
      tellraw @a {"text":"ok","color":"green"};
  }
  

• conditional blocks (if/else if/else statements):

  function "conditional" {
      if "entity @s[type=minecraft:player]" {
          say Player detected!;
          effect give @s minecraft:glowing 5 1;
      } else if "entity @s[type=minecraft:zombie]" {
          say Zombie detected!;
          effect give @s minecraft:poison 5 1;
      } else {
          say Unknown entity;
      }
  }
  

• while loops (repetitive execution):

  function "countdown" {
      scoreboard players set @s counter 5;
      while "score @s counter matches 1.." {
          say Counter: @s counter;
          scoreboard players remove @s counter 1;
      }
  }
  

• for loops (entity iteration):

  function "player_effects" {
      for player in @e[type=minecraft:player] {
          say Processing player: @s;
          effect give @s minecraft:speed 10 1;
      }
  }
  

• function calls (one function invoking another with fully qualified ID):

  function "outer" {
      say I will call another function;
      function example:hello;
  }
  

• hooks (namespaced ids required):

  on_load "example:hello";
  on_tick "example:hello";
  

• tags (supported registries: function, item, block, entity_type, fluid, game_event):

  tag function "minecraft:tick" {
      add "example:hello";
  }
  

  The parser accepts an optional replace flag on the header (e.g. tag function "minecraft:tick" replace {) but replacement behavior is controlled by the pack writer.
• comments start with // or /* */. Hashes inside quoted strings are preserved.
• whitespace: empty lines are ignored; explicit block boundaries using curly braces { and }; statement termination using semicolons ;.

Inside a function block, every non-empty line is emitted almost verbatim as a Minecraft command. Comments are stripped out and multi-line commands are automatically wrapped. See below for details.

Comments

MDL supports modern JavaScript-style comments:

• Full-line comments (a line starting with //) are ignored by the parser.
• Block comments (/* */) are supported for multi-line comments.
• Inline # characters are preserved inside function bodies, so you can still use them the way mcfunction normally allows.

Example:

// Comment Demo - Testing comments
pack "Comment Demo" description "Testing comments";

namespace "demo";

function "comments" {
    // This whole line is ignored by MDL
    say Hello; // This inline comment is preserved
    tellraw @a {"text":"World","color":"blue"}; // Inline too!
    
    /* This is a block comment
       that spans multiple lines
       and is ignored by the parser */
}

When compiled, the resulting function looks like:

say Hello # This inline comment is preserved
tellraw @a {"text":"World","color":"blue"} # Inline too!

Notice how the full-line // and block comments never make it into the .mcfunction, but the inline ones do.

---

Control Flow

MDL supports conditional blocks and loops for advanced control flow.

Conditional Blocks

MDL supports if/else if/else statements for conditional execution:

function "conditional_example" {
    if "entity @s[type=minecraft:player]" {
        say Player detected!;
        effect give @s minecraft:glowing 5 1;
    } else if "entity @s[type=minecraft:zombie]" {
        say Zombie detected!;
        effect give @s minecraft:poison 5 1;
    } else if "entity @s[type=minecraft:creeper]" {
        say Creeper detected!;
        effect give @s minecraft:resistance 5 1;
    } else {
        say Unknown entity;
        effect give @s minecraft:slowness 5 1;
    }
}

Rules:

• Conditions must be valid Minecraft selector syntax
• Explicit block boundaries: Conditional blocks use curly braces { and }
• Statement termination: All commands must end with semicolons ;
• You can have multiple else if blocks
• The else block is optional
• Conditional blocks are compiled to separate functions and called with execute commands
• Proper logic: else if blocks only execute if previous conditions were false

While Loops

MDL supports while loops for repetitive execution:

function "while_example" {
    scoreboard players set @s counter 5;
    while "score @s counter matches 1.." {
        say Counter: @s counter;
        scoreboard players remove @s counter 1;
        say Decremented counter;
    }
}

Rules:

• Conditions must be valid Minecraft selector syntax
• Explicit block boundaries: While loops use curly braces { and }
• Statement termination: All commands must end with semicolons ;
• While loops continue until the condition becomes false
• Important: Ensure your loop body modifies the condition to avoid infinite loops

For Loops

MDL supports for loops for iterating over entity collections:

function "for_example" {
    tag @e[type=minecraft:player] add players;
    for player in @e[tag=players] {
        say Processing player: @s;
        effect give @s minecraft:speed 10 1;
        tellraw @s {"text":"You got speed!","color":"green"};
    }
}

Rules:

• Collection must be a valid Minecraft entity selector
• Explicit block boundaries: For loops use curly braces { and }
• Statement termination: All commands must end with semicolons ;
• For loops iterate over each entity in the collection
• Efficient execution: Each conditional block becomes a separate function for optimal performance

---

Multi-line Commands

Long JSON commands can be split across multiple lines with a trailing backslash \.
MDL will join them back together before writing the final .mcfunction.

Example:

// Multi-line Demo
pack "Multi-line Demo";

namespace "demo";

function "multiline" {
    tellraw @a \
        {"text":"This text is really, really long so we split it",\
         "color":"gold"};
}

When compiled, the function is a single line:

tellraw @a {"text":"This text is really, really long so we split it","color":"gold"}

---

🎯 FULL example (nested calls + multi-namespace)

// mypack.mdl - minimal example for Minecraft Datapack Language
pack "Minecraft Datapack Language" description "Example datapack" pack_format 82 min_format [82, 0] max_format [82, 1] min_engine_version "1.21.4";

namespace "example";

function "inner" {
    say [example:inner] This is the inner function;
    tellraw @a {"text":"Running inner","color":"yellow"};
}

function "hello" {
    say [example:hello] Outer says hi;
    function example:inner;
    tellraw @a {"text":"Back in hello","color":"aqua"};
}

// Hook the function into load and tick
on_load "example:hello";
on_tick "example:hello";

// Second namespace with a cross-namespace call
namespace "util";

function "helper" {
    say [util:helper] Helping out...;
}

function "boss" {
    say [util:boss] Calling example:hello then util:helper;
    function example:hello;
    function util:helper;
}

// Run boss every tick as well
on_tick "util:boss";

// Function tag examples
tag function "minecraft:load" {
    add "example:hello";
}

tag function "minecraft:tick" {
    add "example:hello";
    add "util:boss";
}

// Data tag examples across registries
tag item "example:swords" {
    add "minecraft:diamond_sword";
    add "minecraft:netherite_sword";
}

tag block "example:glassy" {
    add "minecraft:glass";
    add "minecraft:tinted_glass";
}

What this demonstrates

• Nested-like function composition (function example:inner inside function "hello").
• Multiple namespaces (example, util) calling each other with fully-qualified IDs.
• Lifecycle hooks (on_load, on_tick) on both example:hello and util:boss.
• Function tags to participate in vanilla tags (minecraft:load, minecraft:tick).
• Data tags (item, block) in addition to function tags.

---

🐍 Python API equivalent

from minecraft_datapack_language import Pack

def build_pack():
    p = Pack(name="Minecraft Datapack Language",
             description="Example datapack",
             pack_format=48)

    ex = p.namespace("example")
    ex.function("inner",
        'say [example:inner] This is the inner function',
        'tellraw @a {"text":"Running inner","color":"yellow"}'
    )
    ex.function("hello",
        'say [example:hello] Outer says hi',
        'function example:inner',
        'tellraw @a {"text":"Back in hello","color":"aqua"}'
    )

    # Hooks for example namespace
    p.on_load("example:hello")
    p.on_tick("example:hello")

    util = p.namespace("util")
    util.function("helper",
        'say [util:helper] Helping out...'
    )
    util.function("boss",
        'say [util:boss] Calling example:hello then util:helper',
        'function example:hello',
        'function util:helper'
    )

    # Tick hook for util namespace
    p.on_tick("util:boss")

    # Function tags
    p.tag("function", "minecraft:load", values=["example:hello"])
    p.tag("function", "minecraft:tick", values=["example:hello", "util:boss"])

    # Data tags
    p.tag("item",  "example:swords", values=["minecraft:diamond_sword", "minecraft:netherite_sword"])
    p.tag("block", "example:glassy", values=["minecraft:glass", "minecraft:tinted_glass"])

    return p

Build it:

python - <<'PY'
from my_pack_module import build_pack
from minecraft_datapack_language.cli import main as M
# write to dist/ with a wrapper folder name 'mypack'
p = build_pack()
M(['build', '--py-object', 'my_pack_module:build_pack', '-o', 'dist', '--wrapper', 'mypack', '--pack-format', '48'])
PY

---

🔧 VS Code Extension

Get syntax highlighting, linting, and build commands for .mdl files in VS Code, Cursor, and other VS Code-based editors.

Quick Install

1. Download from GitHub Releases
2. Install the .vsix file:
   • Open VS Code/Cursor
   • Go to Extensions (Ctrl+Shift+X)
   • Click "..." → "Install from VSIX..."
   • Choose the downloaded .vsix file

Features

• Syntax highlighting for .mdl files
• Real-time linting with error detection
• Build commands: MDL: Build current file and MDL: Check Workspace
• Workspace validation for multi-file projects

Development Setup

cd vscode-extension/
npm i
# Press F5 to launch the Extension Dev Host

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🚀 CI & Releases

• CI runs on push/PR across Linux/macOS/Windows and uploads artifacts.
• Release is triggered by pushing a tag like v1.0.0 or via the Release workflow manually.
• Versions are derived from git tags via setuptools-scm; tag vX.Y.Z → package version X.Y.Z.

Local release helper

# requires GitHub CLI: gh auth login
./scripts/release.sh patch  "Fixes"
./scripts/release.sh minor  "Features"
./scripts/release.sh major  "Breaking"
./scripts/release.sh v1.2.3 "Exact version"