MCPInstall

blockbench-plugins

Blockbench plugin/extension development for the 3D modeling tool. Use when creating, modifying, or debugging JavaScript plugins for Blockbench including actions, dialogs, panels, menus, toolbars, model manipulation, animation APIs, and custom formats/codecs. Triggers on Blockbench plugin, Blockbench extension, Blockbench API, BBPlugin, model editor plugin, or 3D modeling tool extension.

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Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/jasonjgardner/blockbench-mcp-project --skill blockbench-plugins
  1. 01

    Install

    Run the command in your project. The CLI asks which agents to install for.

  2. 02

    Describe the task

    Ask your agent for something this skill covers. It loads blockbench-plugins automatically when relevant.

  3. 03

    Review the result

    The agent follows the SKILL.md steps, scripts and references bundled with the skill.

SKILL.md

The instructions your agent reads when the skill is triggered.

Blockbench Plugin Development

Overview

Blockbench runs on desktop and the web, exposing host APIs and bundled rendering/UI libraries to plugins. Verify the target host version and its types before choosing APIs; plugin variable isolation does not imply unrestricted native-module or filesystem access. Prefer the current generated API reference and the target checkout when older wiki examples disagree with the host. Set variant and min_version to the environments actually verified.

For model format decisions, UV units, rig distinctions and export handoffs, see format and delivery guidance. A format feature flag advertises host behavior; it does not implement missing validation or runtime serialization in a custom codec.

Quick Reference

TaskApproach
Create clickable commandnew Action() - add to menus/toolbars
Show form/dialognew Dialog() with form fields
Add sidebar panelnew Panel() with Vue component
Modify model elementsUse Undo.initEdit() → modify → Undo.finishEdit()
Custom import/exportnew Codec() + new ModelFormat()
React to changesBlockbench.on('event_name', callback)

Plugin File Structure

plugins/
└── my_plugin/
    ├── my_plugin.js      # Main file (required, ID must match filename)
    ├── about.md          # Extended docs (optional)
    └── icon.png          # 48x48 icon (optional)

Plugin Registration Template

(function() {
    // Store references for cleanup
    let myAction, myPanel, myDialog, eventCallback;
    
    Plugin.register('my_plugin', {
        title: 'My Plugin',
        author: 'Author Name',
        description: 'Short description',
        icon: 'extension',            // Material icon name
        version: '1.0.0',
        variant: 'both',              // 'desktop', 'web', or 'both'
        min_version: '4.8.0',
        tags: ['Utility'],
        
        onload() {
            // Initialize all components here
        },
        
        onunload() {
            // CRITICAL: Delete ALL components here
        },
        
        oninstall() {
            Blockbench.showQuickMessage('Installed!');
        }
    });
})();

Actions

Actions are clickable commands for menus, toolbars, and keybindings.

myAction = new Action('my_action_id', {
    name: 'Action Name',
    description: 'Tooltip text',
    icon: 'star',
    category: 'edit',                 // For keybind settings
    
    condition: () => Cube.selected.length > 0,
    
    keybind: new Keybind({ key: 'k', ctrl: true }),
    
    click(event) {
        // Action logic
    }
});

MenuBar.addAction(myAction, 'filter');  // Add to Filter menu

// Cleanup
myAction.delete();

Menu locations: 'file', 'edit', 'transform', 'filter', 'tools', 'view', 'help'

Action variants:

// Toggle (on/off state)
new Toggle('toggle_id', {
    name: 'Feature',
    default: false,
    onChange(value) { /* handle */ }
});

// Tool (viewport interaction)
new Tool('tool_id', {
    name: 'My Tool',
    cursor: 'crosshair',
    onCanvasClick(data) { /* handle */ },
    onCanvasDrag(data) { /* handle */ }
});

Dialogs

myDialog = new Dialog({
    id: 'my_dialog',
    title: 'Dialog Title',
    width: 540,
    
    form: {
        name: { label: 'Name', type: 'text', value: 'default' },
        count: { label: 'Count', type: 'number', value: 10, min: 1, max: 100 },
        enabled: { label: 'Enabled', type: 'checkbox', value: true },
        mode: {
            label: 'Mode',
            type: 'select',
            options: { a: 'Option A', b: 'Option B' },
            value: 'a'
        },
        color: { label: 'Color', type: 'color', value: '#ff0000' },
        // Conditional field
        advanced: {
            label: 'Advanced',
            type: 'text',
            condition: (form) => form.enabled
        }
    },
    
    onConfirm(formData) {
        console.log(formData.name, formData.count);
        this.hide();
    }
});

myDialog.show();

// Quick dialogs
Blockbench.textPrompt('Enter Value', 'default', (text) => { });
Blockbench.showMessageBox({ title: 'Alert', message: 'Text', buttons: ['OK'] });

Panels

Panels appear in sidebars with Vue components.

myPanel = new Panel('my_panel', {
    name: 'My Panel',
    icon: 'dashboard',
    condition: () => Format.animation_mode,
    
    default_position: {
        slot: 'left_bar',             // 'left_bar', 'right_bar', 'bottom'
        height: 300
    },
    
    component: {
        template: `
            <div>
                <h3>{{ title }}</h3>
                <ul><li v-for="item in items">{{ item.name }}</li></ul>
                <button @click="refresh">Refresh</button>
            </div>
        `,
        data() {
            return { title: 'Items', items: [] };
        },
        methods: {
            refresh() {
                this.items = Cube.selected.map(c => ({ name: c.name }));
            }
        }
    }
});

// Cleanup
myPanel.delete();

Model Manipulation (with Undo)

Register persistent project edits with native Undo, including every affected aspect. Validate targets and stage asynchronous input before opening a transaction; cancel/restore it on failure. Native actions or painting APIs may own their own transaction, so do not add a competing nested one. Read-only inspection, camera movement and file writes are not equivalent to undoable model mutations. See Undo documentation.

// Start tracking
Undo.initEdit({ elements: Cube.selected });

// Modify elements
Cube.selected.forEach(cube => {
    cube.from[0] += 5;
    cube.to[1] = 20;
    cube.rotation[1] = 45;
});

// Update view
Canvas.updateView({
    elements: Cube.selected,
    element_aspects: { geometry: true, transform: true }
});

// Commit
Undo.finishEdit('Move cubes');

Creating Elements

Creation must record the new objects at transaction completion, not only an empty initial list:

Undo.initEdit({ elements: [], outliner: true });
const createdCube = new Cube({ name: 'body_geo', from: [-4, 0, -2], to: [4, 12, 2] }).init();
Undo.finishEdit('Add body cube', { elements: [createdCube], outliner: true });
Canvas.updateAll();

The snippets below illustrate individual host constructors; place them inside the appropriate transaction when changing an existing project. A group's origin is a pivot; parenting does not add that origin as a translation to cube bounds.

// Cube
let cube = new Cube({
    name: 'my_cube',
    from: [0, 0, 0],
    to: [16, 16, 16],
    origin: [8, 8, 8],
    rotation: [0, 45, 0]
}).init();
cube.addTo(Group.selected[0]);  // Add to group

// Group (bone)
let group = new Group({
    name: 'bone_arm',
    origin: [0, 12, 0]
}).init();
group.addTo();  // Add to root

// Texture
let texture = new Texture({ name: 'my_texture' });
texture.fromPath('/path/to/file.png');  // or .fromDataURL()
texture.add(true);  // true = add to undo

Global Collections

CollectionDescription
Cube.all / Cube.selectedAll cubes / selected cubes
Group.all / Group.selectedAll groups / selected groups
Mesh.all / Mesh.selectedAll meshes / selected meshes
Texture.all / Texture.selectedAll textures / selected
Animation.all / Animation.selectedAll animations / selected
Outliner.elementsAll outliner elements

Event System

// Subscribe
eventCallback = (data) => { /* handle */ };
Blockbench.on('update_selection', eventCallback);

// Unsubscribe (use SAME function reference)
Blockbench.removeListener('update_selection', eventCallback);

Common events: update_selection, select_project, new_project, load_project, save_project, close_project, add_cube, add_group, add_texture, add_animation, select_animation, render_frame, undo, redo, finish_edit

See references/events.md for full list.

Custom Menus

let menu = new Menu([
    'existing_action_id',
    myAction,
    '_',  // Separator
    {
        name: 'Custom Item',
        icon: 'star',
        click() { /* handle */ }
    },
    {
        name: 'Submenu',
        children: [ /* more items */ ]
    }
]);

menu.open(event);  // Open at mouse position

Format and Codec (Import/Export)

const myCodec = new Codec('my_codec', {
    name: 'My Format',
    extension: 'mymodel',
    
    compile(options) {
        // Model → file content
        let data = { bones: [] };
        Group.all.forEach(g => {
            data.bones.push({
                name: g.name,
                pivot: g.origin,
                cubes: g.children.filter(c => c instanceof Cube).map(c => ({
                    from: c.from, to: c.to
                }))
            });
        });
        return JSON.stringify(data, null, 2);
    },
    
    parse(content, path) {
        // File content → model
        let data = JSON.parse(content);
        newProject(myFormat);
        data.bones.forEach(b => {
            let group = new Group({ name: b.name, origin: b.pivot }).init();
            b.cubes.forEach(c => {
                new Cube({ from: c.from, to: c.to }).init().addTo(group);
            });
        });
        Canvas.updateAll();
    }
});

const myFormat = new ModelFormat('my_format', {
    id: 'my_format',
    name: 'My Format',
    icon: 'icon_name',
    codec: myCodec,
    box_uv: true,
    bone_rig: true,
    animation_mode: true
});

// Cleanup
myFormat.delete();
myCodec.delete();

Condition Patterns

// Function
condition: () => Format.id === 'bedrock' && Cube.selected.length > 0

// Object (combined with AND)
condition: {
    formats: ['bedrock', 'java_block'],
    modes: ['edit', 'paint'],
    project: true,
    selected: { cube: 1 },
    method: () => customCheck()
}

Code Style Conventions

TypeConventionExamples
ClassesPascalCaseOutlinerElement, Animation
MethodscamelCaseupdateTransform, getSelectedFaces
Propertiessnake_casedata_points, uv_offset
Event/Action IDssnake_caseselect_project, my_action

Critical Cleanup Pattern

MUST delete all components in onunload() to prevent memory leaks.

let action, panel, dialog, toolbar, format, codec, eventCallback, css;

Plugin.register('my_plugin', {
    onload() {
        action = new Action('id', { /* ... */ });
        panel = new Panel('id', { /* ... */ });
        format = new ModelFormat('id', { /* ... */ });
        codec = new Codec('id', { /* ... */ });
        
        eventCallback = (data) => { };
        Blockbench.on('update_selection', eventCallback);
        
        css = Blockbench.addCSS('.my-class { color: blue; }');
    },
    
    onunload() {
        action.delete();
        panel.delete();
        format.delete();
        codec.delete();
        Blockbench.removeListener('update_selection', eventCallback);
        css.delete();
    }
});

Anti-Patterns

// ❌ No stored reference = memory leak
onload() { new Action('leaked', { }); }

// ❌ No Undo = users can't reverse
Cube.selected.forEach(c => c.from[0] += 1);

// ❌ Bundling THREE.js (already global)
import * as THREE from 'three';

// ❌ Global pollution
window.myData = {};

Built-in Libraries (Do Not Bundle)

  • THREE — Three.js 3D rendering
  • Vue — host-provided reactive UI; match the host's supported component API
  • JSZip — ZIP handling
  • marked — Markdown parsing
  • Molang — Molang expression parser

Icons

icon: 'star'              // Material icon
icon: 'fa-bone'           // Font Awesome
icon: 'icon-player'       // Blockbench custom
icon: 'data:image/...'    // Base64 image

TypeScript Setup

npm i --save-dev blockbench-types
/// <reference types="blockbench-types" />

Template Files

  • assets/plugin_template.js — Complete starter plugin
  • assets/format_plugin.js — Custom format/codec example

References

  • references/events.md — Event reference; confirm version-specific events in the target host
  • references/api.md — Local API examples
  • references/elements.md — Element types and properties
  • Creating a Plugin — Official registration, lifecycle and development guidance
  • Generated API reference — Current host types and comments

Verify a plugin edit with a representative project: expected data/preview, Undo then Redo, and unload/reload cleanup. For formats/codecs, check a representative export and reimport, including UV dimensions, hierarchy, names, texture references and animation behavior where supported. Passing compilation does not exercise native editor state or serialized output.

FAQ

What does the blockbench-plugins skill do?

Blockbench plugin/extension development for the 3D modeling tool. Use when creating, modifying, or debugging JavaScript plugins for Blockbench including actions, dialogs, panels, menus, toolbars, model manipulation, animation APIs, and custom formats/codecs. Triggers on Blockbench plugin, Blockbench extension, Blockbench API, BBPlugin, model editor plugin, or 3D modeling tool extension.

How do I install blockbench-plugins?

Run npx skills add https://github.com/jasonjgardner/blockbench-mcp-project --skill blockbench-plugins in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/blockbench-plugins/ (personal) or .claude/skills/blockbench-plugins/ (project).

Which AI agents can use blockbench-plugins?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is blockbench-plugins safe to install?

No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.

Who maintains blockbench-plugins?

It is published by jasonjgardner in jasonjgardner/blockbench-mcp-project. It has 654 recorded installs.

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