Imported from David-Li0406/meta-skill-evloving (skill-flow/data/skills-refined-agentskillos-36k/skillsmp/threejs-builder/SKILL.md). Install upstream with npx skills add David-Li0406/meta-skill-evloving --skill threejs-builder. Copyright stays with the author.

Three.js Builder

A focused skill for creating simple, performant Three.js web applications using modern ES module patterns.

Required response headings

Every response must include these headings:

## When to use
## Inputs
## Outputs

Failure-mode template (out of scope)

Use this exact structure when the request is out of scope:

## When to use
- This skill applies to building small Three.js scenes and demos. The current request is out of scope.

## Outputs
- None (out of scope).

## Inputs
- None (out of scope).

Philosophy: The Scene Graph Mental Model

Three.js is built on the scene graph—a hierarchical tree of objects where parent transformations affect children. Understanding this mental model is key to effective 3D web development.

Before creating a Three.js app, ask:

What is the core visual element? (geometry, shape, model)
What interaction does the user need? (none, orbit controls, custom input)
What performance constraints exist? (compact screens, desktop, WebGL capabilities)
What animation brings it to life? (rotation, movement, transitions)

Core principles:

Scene Graph First: Everything added to scene renders. Use Group for hierarchical transforms.
Primitives as Building Blocks: Built-in geometries (Box, Sphere, Torus) cover 80% of simple use cases.
Animation as Transformation: Change position/rotation/scale over time using requestAnimationFrame or renderer.setAnimationLoop.
Performance Through Simplicity: Fewer objects, fewer draw calls, reusable geometries/materials.

Examples

"Create a rotating cube scene with responsive resize handling."
"Set up a basic orbit-controlled camera for a product demo."

Quick Start: Essential Setup

Minimal HTML Template

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Three.js App</title>
    <style>
        * { margin: 0; padding: 0; box-sizing: border-box; }
        body { overflow: hidden; background: #000; }
        canvas { display: block; }
    </style>
</head>
<body>
    <script type="module">
        import * as THREE from 'https://unpkg.com/three@0.160.0/build/three.module.js';

        const scene = new THREE.Scene();
        const camera = new THREE.PerspectiveCamera(75, window.innerWidth / window.innerHeight, 0.1, 1000);
        const renderer = new THREE.WebGLRenderer({ antialias: true });

        renderer.setSize(window.innerWidth, window.innerHeight);
        renderer.setPixelRatio(Math.min(window.devicePixelRatio, 2));
        document.body.appendChild(renderer.domElement);

        camera.position.z = 5;

        renderer.setAnimationLoop((time) => {
            renderer.render(scene, camera);
        });

        window.addEventListener('resize', () => {
            camera.aspect = window.innerWidth / window.innerHeight;
            camera.updateProjectionMatrix();
            renderer.setSize(window.innerWidth, window.innerHeight);
        });
    </script>
</body>
</html>

Geometries

Built-in primitives cover most simple app needs. Use BufferGeometry only for custom shapes.

Common primitives:

BoxGeometry(width, height, depth) - cubes, boxes
SphereGeometry(radius, widthSegments, heightSegments) - balls, planets
CylinderGeometry(radiusTop, radiusBottom, height) - tubes, cylinders
TorusGeometry(radius, tube) - donuts, rings
PlaneGeometry(width, height) - floors, walls, backgrounds
ConeGeometry(radius, height) - spikes, cones
IcosahedronGeometry(radius, detail) - low-poly spheres (detail=0)

Usage:

const geometry = new THREE.BoxGeometry(1, 1, 1);
const material = new THREE.MeshStandardMaterial({ color: 0x44aa88 });
const mesh = new THREE.Mesh(geometry, material);
scene.add(mesh);

Materials

Choose material based on lighting needs and visual style.

Material selection guide:

MeshBasicMaterial - No lighting, flat colors. Use for: UI, wireframes, unlit effects
MeshStandardMaterial - PBR lighting. Default for realistic surfaces
MeshPhysicalMaterial - Advanced PBR with clearcoat, transmission. Glass, water
MeshNormalMaterial - Debug, rainbow colors based on normals
MeshPhongMaterial - Legacy, shininess control. Faster than Standard

Common material properties:

{
    color: 0x44aa88,           // Hex color
    roughness: 0.5,            // 0=glossy, 1=matte (Standard/Physical)
    metalness: 0.0,            // 0=non-metal, 1=metal (Standard/Physical)
    emissive: 0x000000,        // Self-illumination color
    wireframe: false,          // Show edges only
    transparent: false,        // Enable transparency
    opacity: 1.0,              // 0=invisible, 1=opaque (needs transparent:true)
    side: THREE.FrontSide      // FrontSide, BackSide, DoubleSide
}

Lighting

No light = black screen (except BasicMaterial/NormalMaterial).

Light types:

AmbientLight(intensity) - Base illumination everywhere. Use 0.3-0.5
DirectionalLight(color, intensity) - Sun-like, parallel rays. Cast shadows
PointLight(color, intensity, distance) - Light bulb, emits in all directions
SpotLight(color, intensity, angle, penumbra) - Flashlight, cone of light

Typical lighting setup:

const ambientLight = new THREE.AmbientLight(0xffffff, 0.4);
scene.add(ambientLight);

const mainLight = new THREE.DirectionalLight(0xffffff, 1);
mainLight.position.set(5, 10, 7);
scene.add(mainLight);

const fillLight = new THREE.DirectionalLight(0x88ccff, 0.5);
fillLight.position.set(-5, 0, -5);
scene.add(fillLight);

Shadows (advanced, use when needed):

renderer.shadowMap.enabled = true;
renderer.shadowMap.type = THREE.PCFSoftShadowMap;

mainLight.castShadow = true;
mainLight.shadow.mapSize.width = 2048;
mainLight.shadow.mapSize.height = 2048;

mesh.castShadow = true;
mesh.receiveShadow = true;

Animation

Transform objects over time using the animation loop.

Animation patterns:

Continuous rotation:

renderer.setAnimationLoop((time) => {
    mesh.rotation.x = time * 0.001;
    mesh.rotation.y = time * 0.0005;
    renderer.render(scene, camera);
});

Wave/bobbing motion:

renderer.setAnimationLoop((time) => {
    mesh.position.y = Math.sin(time * 0.002) * 0.5;
    renderer.render(scene, camera);
});

Mouse interaction:

const mouse = new THREE.Vector2();

window.addEventListener('mousemove', (event) => {
    mouse.x = (event.clientX / window.innerWidth) * 2 - 1;
    mouse.y = -(event.clientY / window.innerHeight) * 2 + 1;
});

renderer.setAnimationLoop(() => {
    mesh.rotation.x = mouse.y * 0.5;
    mesh.rotation.y = mouse.x * 0.5;
    renderer.render(scene, camera);
});

Camera Controls

Import OrbitControls from examples for interactive camera movement:

<script type="module">
    import * as THREE from 'https://unpkg.com/three@0.160.0/build/three.module.js';
    import { OrbitControls } from 'https://unpkg.com/three@0.160.0/examples/jsm/controls/OrbitControls.js';

    const controls = new OrbitControls(camera, renderer.domElement);
    controls.enableDamping = true;
    controls.dampingFactor = 0.05;

    renderer.setAnimationLoop(() => {
        controls.update();
        renderer.render(scene, camera);
    });
</script>

Common Scene Patterns

Rotating Cube (Hello World)

const geometry = new THREE.BoxGeometry(1, 1, 1);
const material = new THREE.MeshStandardMaterial({ color: 0x00ff88 });
const cube = new THREE.Mesh(geometry, material);
scene.add(cube);

renderer.setAnimationLoop((time) => {
    cube.rotation.x = time * 0.001;
    cube.rotation.y = time * 0.001;
    renderer.render(scene, camera);
});

Floating Particle Field

const particleCount = 1000;
const geometry = new THREE.BufferGeometry();
const positions = new Float32Array(particleCount * 3);

for (let i = 0; i < particleCount * 3; i += 3) {
    positions[i] = (Math.random() - 0.5) * 50;
    positions[i + 1] = (Math.random() - 0.5) * 50;
    positions[i + 2] = (Math.random() - 0.5) * 50;
}

geometry.setAttribute('position', new THREE.BufferAttribute(positions, 3));
const material = new THREE.PointsMaterial({ color: 0xffffff, size: 0.1 });
const particles = new THREE.Points(geometry, material);
scene.add(particles);

Animated Background with Foreground Object

const gridHelper = new THREE.GridHelper(50, 50, 0x444444, 0x222222); // Background grid
scene.add(gridHelper);

const mainGeometry = new THREE.IcosahedronGeometry(1, 0); // Foreground object
const mainMaterial = new THREE.MeshStandardMaterial({
    color: 0xff6600,
    flatShading: true
});
const mainMesh = new THREE.Mesh(mainGeometry, mainMaterial);
scene.add(mainMesh);

Colors

Three.js uses hexadecimal color format: 0xRRGGBB

Common hex colors:

Black: 0x000000, White: 0xffffff
Red: 0xff0000, Green: 0x00ff00, Blue: 0x0000ff
Cyan: 0x00ffff, Magenta: 0xff00ff, Yellow: 0xffff00
Orange: 0xff8800, Purple: 0x8800ff, Pink: 0xff0088

Anti-Patterns to Avoid

Basic Setup Mistakes

❌ Not importing OrbitControls from correct path Why bad: Controls won't load, THREE.OrbitControls is undefined in modern Three.js Better: Use import { OrbitControls } from 'three/addons/controls/OrbitControls.js' or unpkg examples/jsm path

❌ Forgetting to add object to scene Why bad: Object won't render, silent failure Better: Always call scene.add(object) after creating meshes/lights

❌ Using old requestAnimationFrame pattern instead of setAnimationLoop Why bad: More verbose, doesn't handle XR/WebXR automatically Better: renderer.setAnimationLoop((time) => { ... })

Performance Issues

❌ Creating new geometries in animation loop Why bad: Massive memory allocation, frame rate collapse Better: Create geometry once, reuse it. Transform only position/rotation/scale

❌ Using too many segments on primitives Why bad: Unnecessary vertices, GPU overhead Better: Default segments are usually fine. SphereGeometry(1, 32, 16) not SphereGeometry(1, 128, 64)

❌ Not setting pixelRatio cap Why bad: 4K/5K displays run at full resolution, poor performance Better: Math.min(window.devicePixelRatio, 2)

Code Organization

❌ Everything in one giant function Why bad: Hard to modify, hard to debug Better: Separate setup into functions: createScene(), createLights(), createMeshes()

❌ Hardcoding all values Why bad: Difficult to tweak and experiment Better: Define constants at top: const CONFIG = { color: 0x00ff88, speed: 0.001 }

Variation Guidance

IMPORTANT: Each Three.js app should feel unique and context-appropriate.

Vary by scenario:

Portfolio/showcase: Elegant, smooth animations, muted colors
Game/interactive: Bright colors, snappy controls, particle effects
Data visualization: Clean lines, grid helpers, clear labels
Background effect: Subtle, slow movement, dark/gradient backgrounds
Product viewer: Realistic lighting, PBR materials, smooth orbit

Vary visual elements:

Geometry choice: Not everything needs to be a cube. Explore spheres, tori, icosahedra
Material style: Mix flat shaded, glossy, metallic, wireframe
Color palettes: Use complementary, analogous, or monochromatic schemes
Animation style: Rotation, oscillation, wave motion, mouse tracking

Avoid converging on:

Default green cube as first example every time
Same camera angle (front-facing, z=5)
Identical lighting setup (always directional light at 1,1,1)

Remember

Three.js is a tool for interactive 3D on the web.

Effective Three.js apps:

Start with the scene graph mental model
Use primitives as building blocks
Keep animations simple and performant
Vary visual style based on purpose
Import from modern ES module paths

Modern Three.js (r150+) uses ES modules from three package or CDN. CommonJS patterns and global THREE variable are legacy.

For advanced topics (GLTF models, shaders, post-processing), see references/advanced-topics.md.

Claude is capable of creating elegant, performant 3D web experiences. These patterns guide the way—they don't limit the result.

When to use

Use this skill when the task matches its description and triggers.
If the request is outside scope, route to the referenced skill.

Inputs

User request details and any relevant files/links.

Outputs

A structured response or artifact appropriate to the skill.
Include schema_version: 1 if outputs are contract-bound.

Constraints

Redact secrets/PII by default.
Avoid destructive operations without explicit user direction.

Validation

Run any relevant checks or scripts when available.
Fail fast and report errors before proceeding.

Anti-patterns

Avoid vague guidance without concrete steps.
Do not invent results or commands.

Procedure

Clarify scope and inputs.
Execute the core workflow.
Summarize outputs and next steps.

Antipatterns

Do not add features outside the agreed scope.

threejs-builder

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