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playcanvas

PlayCanvas Editor MCP Server

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by playcanvas

set_material_diffuse

Assign RGB color values to the diffuse property of a material in PlayCanvas Editor by specifying an asset ID and a color array.

Instructions

Set diffuse property on a material

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
assetIdYesAn asset ID.
colorYesA 3-channel RGB color

Implementation Reference

  • The handler function for the 'set_material_diffuse' MCP tool. It takes assetId and color parameters and calls wss.call to set the 'diffuse' property on the material asset.
    ({ assetId, color }) => {
        return wss.call('assets:property:set', assetId, 'diffuse', color);
    }
  • RgbSchema defines the input schema for the 'color' parameter of the set_material_diffuse tool as a tuple of three numbers between 0 and 1.
    export const RgbSchema = z.tuple([
        z.number().min(0).max(1).describe('Red'),
        z.number().min(0).max(1).describe('Green'),
        z.number().min(0).max(1).describe('Blue')
    ]).describe('A 3-channel RGB color');
  • AssetIdSchema defines the input schema for the 'assetId' parameter of the set_material_diffuse tool as a nullable integer.
    export const AssetIdSchema = z.number().int().nullable().describe('An asset ID.');
  • The register function that registers the 'set_material_diffuse' tool with the MCP server, including its name, description, input schema, and handler.
    export const register = (mcp: McpServer, wss: WSS) => {
        mcp.tool(
            'set_material_diffuse',
            'Set diffuse property on a material',
            {
                assetId: AssetIdSchema,
                color: RgbSchema
            },
            ({ assetId, color }) => {
                return wss.call('assets:property:set', assetId, 'diffuse', color);
            }
        );
    };
Behavior2/5

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. 'Set' implies a mutation operation, but the description doesn't specify whether this requires specific permissions, if changes are reversible, what happens to existing properties, or any rate limits. This leaves significant gaps in understanding the tool's behavior beyond the basic action.

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 that directly states the tool's purpose without any unnecessary words. It's front-loaded and wastes no space, making it highly concise and well-structured for quick comprehension.

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 complexity of a mutation tool with no annotations and no output schema, the description is incomplete. It doesn't cover behavioral aspects like error handling, return values, or side effects, and while the schema covers parameters well, the overall context for safe and effective use is lacking. This makes it inadequate for a tool that modifies assets.

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?

The input schema has 100% description coverage, with clear documentation for both parameters (assetId and color). The description doesn't add any meaning beyond what the schema provides, such as explaining how the color affects the material or what assetId refers to. Given the high schema coverage, a baseline score of 3 is appropriate as the schema does the heavy lifting.

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

Purpose4/5

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

The description clearly states the verb ('Set') and the resource ('diffuse property on a material'), making the purpose specific and understandable. However, it doesn't distinguish this tool from its siblings (e.g., modify_entities or modify_scene_settings), which might also affect material properties, so it doesn't reach the highest score.

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?

The description provides no guidance on when to use this tool versus alternatives like modify_entities or other material-related tools in the sibling list. It lacks context about prerequisites, such as needing an existing material or asset, and doesn't mention any exclusions or specific scenarios for its use.

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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