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playcanvas

PlayCanvas Editor MCP Server

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by playcanvas

create_entities

Create one or more entities in the PlayCanvas Editor, enabling the definition of properties like name, position, rotation, scale, tags, and components, as well as parent-child hierarchies for 3D application development.

Instructions

Create one or more entities

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
entitiesYesArray of entity hierarchies to create.

Implementation Reference

  • Registration of the MCP tool 'create_entities'. Includes inline input schema validation using Zod and a handler function that proxies the call to the WebSocket server via wss.call('entities:create', entities). This constitutes the full tool implementation in the MCP context.
        'create_entities',
        'Create one or more entities',
        {
            entities: z.array(z.object({
                entity: EntitySchema,
                parent: EntityIdSchema.optional().describe('The parent entity to create the entity under. If not provided, the root entity will be used.')
            })).nonempty().describe('Array of entity hierarchies to create.')
        },
        ({ entities }) => {
            return wss.call('entities:create', entities);
        }
    );
  • The handler function for the 'create_entities' tool, which receives the validated 'entities' input and forwards it to the backend via wss.call('entities:create', entities).
    ({ entities }) => {
        return wss.call('entities:create', entities);
    }
  • Input schema for 'create_entities' tool using Zod: non-empty array of objects with 'entity' (EntitySchema) and optional 'parent' (EntityIdSchema).
    entities: z.array(z.object({
        entity: EntitySchema,
        parent: EntityIdSchema.optional().describe('The parent entity to create the entity under. If not provided, the root entity will be used.')
    })).nonempty().describe('Array of entity hierarchies to create.')
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden of behavioral disclosure. It states 'Create' which implies a write/mutation operation, but doesn't mention permissions needed, whether creation is reversible, rate limits, or what happens on failure (e.g., partial creation). For a complex creation tool with hierarchical data, this is a significant gap in transparency.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, efficient sentence with zero waste. It's appropriately sized for a tool where the schema carries most of the detail, though this conciseness comes at the cost of completeness in other dimensions.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's complexity (hierarchical entity creation with multiple component types), no annotations, and no output schema, the description is inadequate. It doesn't explain what an 'entity' is in this system, how creation interacts with the scene, what the return value looks like, or error conditions. For a foundational creation tool, this leaves too much unexplained.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema fully documents the single parameter 'entities' and its complex nested structure. The description adds no parameter-specific information beyond implying multiplicity ('one or more'), which is already clear from the schema's array type with minItems:1. Baseline 3 is appropriate when the schema does all the work.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose3/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description 'Create one or more entities' states the verb (create) and resource (entities), but is vague about what entities are in this context. It doesn't distinguish from siblings like 'instantiate_template_assets' or 'duplicate_entities', which also create entities through different mechanisms. The purpose is clear at a basic level but lacks specificity.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

No guidance is provided about when to use this tool versus alternatives like 'instantiate_template_assets' (for templated creation) or 'duplicate_entities' (for copying existing ones). The description doesn't mention prerequisites, context, or exclusions, leaving the agent with no usage direction beyond the basic action.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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