Sdk Scenes

Decentraland SDK7 Scene Development

Runtime constraint: Decentraland runs in a QuickJS sandbox. No Node.js APIs (fs, http, path, process). Use executeTask() + fetch() for async work.

Agent Behavioral Guidelines

Before taking any significant action, check whether it falls into one of the four categories below and confirm with the user first.

How to ask: Phrase the question in plain, non-technical language that describes what will happen to the scene, not the underlying command.

Good: "Should I download this tree model into your scene assets?" Bad: "Run curl https://… -o assets/Models/tree.glb?"

1. Changing parcel count or layout

Any modification to scene.parcels in scene.json changes the scene's coordinate space. Entities near the current boundary may end up outside (invisible) or inside the wrong parcel. The user may also have a deployment slot in mind and parcel count needs to match it. Describe the change and its effect before acting:

"To fit the scene you described, I'd need to expand from 1 parcel (16×16 m) to a 2×1 layout (32×16 m). This changes the coordinate bounds for every entity. Should I go ahead?"

2. Fetching assets from external sources

Downloading any file not already in the project — 3D models (.glb), images, audio, video. The user may have their own assets in mind, may not want new files added, or may be targeting a specific visual style. Confirm before downloading:

"I'd like to download a [description] model from [source] and add it to your scene. Should I go ahead?"

For streaming references (AudioStream, VideoPlayer): these don't download files but do add an external URL dependency. Confirm if the URL wasn't provided by the user:

"I'd set up a video stream from [source]. Is that the one you want to use?"

3. Adding a Multiplayer Server

Introduces isServer(), registerMessages(), Storage, EnvVar, or switches to @dcl/sdk@auth-server. This feature requires switching to an alternative SDK branch (@dcl/sdk@auth-server). Many users who want "multiplayer" only need the simpler multiplayer-sync skill (no server). Confirm before implementing:

"To handle multiplayer this way I'd need to add the Multiplayer Server — that requires switching to the @dcl/sdk@auth-server SDK branch instead of the standard one. Is that what you're after, or would simpler peer-to-peer sync work for your use case?"

4. Falling back from the Blender MCP to headless Blender

If mcp__blender__* tools exist in the session but aren't connected (Blender isn't running, add-on disabled), never silently switch to headless Blender CLI — ask first:

"The Blender MCP is set up but Blender isn't running. Want to open Blender so I can work in it live — you'd see the model as it's built and could edit alongside me — or should I do this headless instead?"

The MCP is what makes model work collaborative; a silent fallback removes that choice. If the MCP isn't installed at all, don't ask the user to install it — go headless and just mention the MCP as an option in your report. Full rule in add-3d-models.

General principle

These aren't things the agent should refuse to do — they're things it should communicate about before doing them. If the user confirms, proceed confidently. The goal is transparency, not gatekeeping.

CRITICAL RULE — Composite-first scene authoring

All static entities (models, lights, spawn points) MUST be defined in assets/scene/main.composite, NOT created in TypeScript via engine.addEntity().

TypeScript (src/index.ts) is ONLY for:

• Dynamic behavior (systems, event handlers, state changes)
• Referencing composite entities via getEntityOrNullByName('name') or getEntitiesByTag('tag')
• Entities that are truly runtime-only (spawned/despawned during gameplay)

CRITICAL RULE — Editing an existing composite

If the Creator Hub MCP is available, use it — never hand-edit the file. The Creator Hub ships an MCP server (skill: creator-hub-mcp) whose tools (scene_state, create_entity, set_component, remove_entity, place_smart_item, attach_script, set_scene_settings, …) edit the open scene live, with autosave, undo, and the editor bookkeeping handled for you. It is pre-wired inside the Creator Hub's own AI assistant, and any other MCP-capable tool (Claude Code, Cursor, Codex, Claude Desktop) can connect to it via Settings > Experimental > Expose AI assistant MCP server. Use it for scene.json changes too (set_scene_settings). Editing the file while the scene is open in the Creator Hub loses your work silently: the inspector autosaves by default and regenerates the whole main.composite from its in-memory engine, overwriting the file wholesale — it never re-reads it from disk.

Only when the MCP is not available (no Creator Hub in play, or the user declines to connect it) fall back to editing assets/scene/main.composite directly, and then:

• The scene must NOT be open in the Creator Hub while you edit the file. Ask the user to close the scene first, then reopen it when you are done.
• Scan the file for inspector::Nodes. If present, the user has opened the scene in the Creator Hub at least once and the file is in edit mode: every new entity you add MUST be registered in inspector::Nodes, or it will render in-world but be invisible and un-selectable in the Creator Hub entity tree. See the "Editing an existing composite (edit mode)" section of {baseDir}/../composites/composite-reference.md for the exact procedure.

Individual Skills

This skill is the entry point. The detailed implementation guidance lives in individual topic skills, each installable separately. Install specific ones or use --skill '*' for all.

Scene Setup & Configuration

Skill: create-scene — Scaffolding, scene.json schema, multi-parcel layouts, composite vs TypeScript entity rules.

3D Models

Skill: add-3d-models — Loading .glb/.gltf with GltfContainer, positioning, colliders, and browsing the free asset catalogs (8,800+ models). Also authoring and editing custom models by driving Blender (headless CLI or Blender MCP).

Animations & Tweens

Skill: animations-tweens — GLTF animation clips with Animator, programmatic Tween and TweenSequence, easing functions.

Materials & Rendering

Skill: advanced-rendering — PBR materials, TextShape, Billboard, VisibilityComponent, texture modes.

Lighting & Environment

Skill: lighting-environment — Point/spot lights, shadows, SkyboxTime (day/night cycle), emissive materials.

Particle Systems

Skill: particle-system — ParticleSystem component for fire, smoke, sparks, snow, rain, magic, fireworks. Emitter shapes (Point/Sphere/Cone/Box), continuous rate vs Burst emission, gravity, sprite-sheet animation, blend modes.

Click & Proximity Interactivity

Skill: add-interactivity — pointerEventsSystem, trigger areas, raycasting. For polling-based input see advanced-input.

Advanced Input & Movement Control

Skill: advanced-input — inputSystem polling, WASD-controlled entities, InputModifier, PointerLock, PrimaryPointerInfo, TouchScreenControls (mobile on-screen joystick/crosshair/buttons).

Player & Avatar

Skill: player-avatar — Player position/profile, emotes, wearables, AvatarAttach, AvatarModifierArea.

NPCs

Skill: npcs — AvatarShape NPCs and the NPC Toolkit library for GLB-based NPCs with dialogue and state machines.

Player Physics

Skill: player-physics — Impulse forces, knockback, repulsion fields.

Camera

Skill: camera-control — Camera state, CameraModeArea, VirtualCamera for cinematic shots.

Screen-Space UI

Skill: build-ui — React ECS components for 2D screen-space UI overlays: layout, text, images, buttons, inputs.

Skill: editable-ui — Write that UI so the Creator Hub's 2D UI editor (UI Designer) can read and edit it: the src/ui/ file-per-component layout, the state/props binding surface, useInteraction style layers, @ui-action handlers, and the driver pattern that keeps animation outside the editor's reach. Use whenever the user wants UI editable in the Creator Hub, or wants an existing coded UI adapted for it.

Audio & Video

Skill: audio-video — AudioSource, AudioStream, VideoPlayer, media permissions.

Audio Analysis (Reactive Visualizers)

Skill: audio-analysis — AudioAnalysis component for real-time amplitude + 8-band frequency data from any AudioSource/AudioStream/VideoPlayer. Drive scale, color, lights, and particles from music. Unity-explorer only.

Blockchain & NFTs

Skill: nft-blockchain — NftShape, wallet checks, token gating, signed requests, smart contracts.

Multiplayer (CRDT, no server)

Skill: multiplayer-sync — syncEntity for peer-to-peer sync, MessageBus, parent-child sync.

Multiplayer Server

Skill: authoritative-server — Headless server, isServer(), registerMessages(), Storage, EnvVar. Requires @dcl/sdk@auth-server.

Script Components (Creator Hub)

Skill: script-components — Writing .ts script files for the Creator Hub Script component, constructor parameters, @action JSDoc tags (never decorator syntax).

Creator Hub MCP (live scene editing)

Skill: creator-hub-mcp — Editing the scene that is open in the Creator Hub through its MCP server: tool catalog (scene_state, create_entity, set_component, place_smart_item, attach_script, set_scene_settings, launch_preview, …), read-before-write workflow, placing catalog items and custom models, and how to connect an external agent (Claude Code, Cursor, Codex) to it. The preferred way to change entities whenever the scene is open in the Creator Hub — instead of editing main.composite.

Testing in the Explorer (MCP)

Skill: unity-explorer-mcp — Driving a running Decentraland Explorer through its MCP automation server: launch, camera and player movement, screenshots, logs, performance stats. Inside the Creator Hub the same tools arrive through the Creator Hub MCP's launch_preview / explorer_*.

Async, HTTP, WebSocket, Timers

Skill: scene-runtime — executeTask, fetch, signedFetch, WebSocket, timers, realm/scene info, restricted actions.

Scene Optimization

Skill: optimize-scene — Scene limits, object pooling, LOD, texture optimization, system throttling.

Game Design

Skill: game-design — DCL design philosophy, state management, UX guidelines, game loop archetypes, MVP planning.

Deployment

• Skill: deploy-scene — Genesis City deployment, dcl deploy, troubleshooting.
• Skill: deploy-worlds — Personal Worlds, worldConfiguration, ENS/DCL NAME requirements.

SDK6 → SDK7 Migration

Skill: migrate-sdk6-to-sdk7 — Port legacy decentraland-ecs scenes to SDK7. Conceptual ECS shift (entities as IDs, data-only components, mutable/immutable access), full API mapping (new Entity() → engine.addEntity(), GLTFShape → GltfContainer, OnPointerDown → pointerEventsSystem, ISystem classes → free functions, Input.instance → inputSystem, etc.), and an annotated before/after example.

Shared References

These reference files are used across multiple skills. Load them when you need detailed component APIs, validation rules, or asset catalogs.

Components Reference

Reference: {baseDir}/references/components-reference.md Quick-reference of key fields, types, and defaults for the SDK7 components you'll commonly use. For a component's complete field list, consult its dedicated skill or the SDK typings.

Entity Validation Rules

Reference: {baseDir}/../create-scene/references/entity-validation-rules.md Rules for validating entity component combinations — which components require each other, mutual exclusions, and common misconfigurations. Apply to both composite and TypeScript entities.

Free Asset Catalogs

• 3D Models (8,800+ models): {baseDir}/../add-3d-models/references/model-catalog.md — optimized 3D models with descriptions, dimensions, animations, and download URLs
• Audio (50 sounds): {baseDir}/../audio-video/references/audio-catalog.md — Music, Ambient, SFX, Game Mechanics, UI sounds

Composites

Reference: {baseDir}/../composites/composite-reference.md The .composite JSON format for declaring initial scene entities. Includes getEntityOrNullByName and getEntitiesByTag patterns for fetching composite entities in TypeScript.

Library References

• NPC Toolkit: {baseDir}/../npcs/references/npc-library.mdc — GLB-based NPCs with dialogue, movement, state machines
• Blockchain/NFT patterns: {baseDir}/../nft-blockchain/references/blockchain-patterns.md — NFT display, wallet checks, MANA operations, currency/NFT transactions, marketplace integration (dcl-crypto-toolkit)

How to use

1. Identify the topic from the user's request
2. Load the corresponding skill — it contains the full API, code patterns, and rules
3. For broad requests spanning multiple topics, load each relevant skill
4. For asset discovery, load the relevant catalog and suggest specific assets before fetching any