Minecraft Bedrock add-ons are split into packs: a behavior pack (logic, entities, scripts) and usually a matching resource pack (textures, models, sounds). Scripting lives inside a behavior pack and is powered by the @minecraft/server module, Mojang's own JavaScript/TypeScript API, run inside the game.

Folder layout

Behavior packs live under your game's development_behavior_packs folder so they hot-reload with /reload.

development_behavior_packs/
  my_addon_bp/
    manifest.json
    scripts/
      main.js
    pack_icon.png

Find the folder: - Windows: %localappdata%\Packages\Microsoft.MinecraftUWP_8wekyb3d8bbwe\LocalState\games\com.mojang\development_behavior_packs - Preview/Education editions use a similarly named package folder, search for com.mojang.

manifest.json

Every pack needs a manifest declaring its modules. A scripting-enabled behavior pack needs a data module and a script module, plus a dependency on the @minecraft/server API:

{
  "format_version": 2,
  "header": {
    "name": "My Addon",
    "description": "Custom scripted systems",
    "uuid": "3f1b1e2a-2222-4c3e-9a11-000000000001",
    "version": [1, 0, 0],
    "min_engine_version": [1, 21, 0]
  },
  "modules": [
    {
      "type": "data",
      "uuid": "3f1b1e2a-2222-4c3e-9a11-000000000002",
      "version": [1, 0, 0]
    },
    {
      "type": "script",
      "language": "javascript",
      "uuid": "3f1b1e2a-2222-4c3e-9a11-000000000003",
      "version": [1, 0, 0],
      "entry": "scripts/main.js"
    }
  ],
  "dependencies": [
    { "module_name": "@minecraft/server", "version": "1.15.0" },
    { "module_name": "@minecraft/server-ui", "version": "1.2.0" }
  ]
}

Generate fresh UUIDs (e.g. with uuidgen or an online v4 generator), never reuse the sample ones above, or Minecraft will treat two different packs as the same pack.

Your first script

import { world, system } from "@minecraft/server";

world.afterEvents.playerSpawn.subscribe((event) => {
  const { player, initialSpawn } = event;
  if (initialSpawn) {
    player.sendMessage("§a[Addon]§r Welcome, " + player.name + "!");
  }
});

system.runInterval(() => {
  world.sendMessage("Tick check-in every 5 seconds");
}, 100); // 100 ticks = 5s (20 ticks/sec)

Enable the pack on a world (must turn on Beta APIs under Experiments), then run /reload in-game while you edit, no restart needed.

TypeScript instead of raw JS

Most real projects use TypeScript + esbuild/webpack to bundle down to a single .js your pack loads, so you get autocomplete against Mojang's type defs.

npm init -y
npm i -D typescript esbuild @minecraft/server @minecraft/server-ui

tsconfig.json:

{
  "compilerOptions": {
    "target": "ES2020",
    "module": "ES2020",
    "moduleResolution": "node",
    "strict": true,
    "outDir": "dist"
  }
}

Bundle command (drop the output straight into your pack's scripts/ folder):

npx esbuild src/main.ts --bundle --outfile=development_behavior_packs/my_addon_bp/scripts/main.js --external:@minecraft/server --external:@minecraft/server-ui --format=esm

Key modules you'll import constantly

Debugging

• console.warn(...) / console.error(...) show up in the Content Log (enable it under Settings → Creator).
• Use the Script Debugger in a code editor (VS Code + the "Minecraft Bedrock Edition" extension) to set real breakpoints against a running world.
• world.sendMessage() is the fastest "print statement" for quick checks.

Next: Custom Commands & Events or straight to Forms & UI if you want menus first.