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boshyxd

Roblox Studio MCP Server

set_calculated_property

Use mathematical formulas and variables to dynamically set properties for Roblox Studio instances. Specify paths, property names, and formulas to automate property adjustments.

Instructions

Set properties using mathematical formulas and variables

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
formulaYesMathematical formula (e.g., "Position.magnitude * 2", "index * 50")
pathsYesArray of instance paths to modify
propertyNameYesName of the property to set
variablesNoAdditional variables for the formula

Implementation Reference

  • The main execution handler for the set_calculated_property tool. It validates inputs, sends a request to the Studio bridge API endpoint '/api/set-calculated-property', and formats the response as MCP content.
    async setCalculatedProperty(
      paths: string[], 
      propertyName: string, 
      formula: string,
      variables?: Record<string, any>
    ) {
      if (!paths || paths.length === 0 || !propertyName || !formula) {
        throw new Error('Paths, property name, and formula are required for set_calculated_property');
      }
      const response = await this.client.request('/api/set-calculated-property', { 
        paths, 
        propertyName, 
        formula,
        variables
      });
      return {
        content: [
          {
            type: 'text',
            text: JSON.stringify(response, null, 2)
          }
        ]
      };
    }
  • The input schema definition registered for the set_calculated_property tool in the MCP ListTools response, defining parameters and validation rules.
      name: 'set_calculated_property',
      description: 'Set properties using mathematical formulas and variables',
      inputSchema: {
        type: 'object',
        properties: {
          paths: {
            type: 'array',
            items: { type: 'string' },
            description: 'Array of instance paths to modify'
          },
          propertyName: {
            type: 'string',
            description: 'Name of the property to set'
          },
          formula: {
            type: 'string',
            description: 'Mathematical formula (e.g., "Position.magnitude * 2", "index * 50")'
          },
          variables: {
            type: 'object',
            description: 'Additional variables for the formula'
          }
        },
        required: ['paths', 'propertyName', 'formula']
      }
    },
  • src/index.ts:704-705 (registration)
    The dispatch registration in the CallToolRequestSchema handler's switch statement, routing tool calls to the RobloxStudioTools.setCalculatedProperty method.
    case 'set_calculated_property':
      return await this.tools.setCalculatedProperty((args as any)?.paths as string[], (args as any)?.propertyName as string, (args as any)?.formula as string, (args as any)?.variables);
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. While it indicates this is a mutation tool ('Set properties'), it lacks critical details: it doesn't specify what happens if the formula fails, whether changes are reversible, what permissions are required, or how the tool handles errors. For a mutation tool with zero annotation coverage, 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 extremely concise and front-loaded with a single sentence that captures the core functionality: 'Set properties using mathematical formulas and variables'. There is no wasted language or redundancy, making it efficient and easy to parse for an AI agent.

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 4 parameters, no annotations, and no output schema, the description is incomplete. It fails to address behavioral aspects like error handling, side effects, or return values, and doesn't provide usage context relative to siblings. While the schema covers parameters well, the overall tool understanding remains inadequate for safe and effective use.

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 description mentions 'mathematical formulas and variables', which loosely relates to the 'formula' and 'variables' parameters, but adds minimal semantic value beyond what the schema already provides. With 100% schema description coverage, the baseline is 3, as the schema fully documents all parameters (formula, paths, propertyName, variables) with clear descriptions. The description doesn't compensate with additional insights like formula syntax rules or variable usage examples.

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 tool's purpose: 'Set properties using mathematical formulas and variables'. It specifies the action (set), the target (properties), and the method (mathematical formulas and variables). However, it doesn't explicitly distinguish this tool from sibling tools like 'set_property' or 'mass_set_property', which likely have different approaches to setting properties.

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. It doesn't mention sibling tools like 'set_property' (which might set properties directly without formulas) or 'mass_set_property' (which might handle multiple properties at once), nor does it specify prerequisites, exclusions, or ideal scenarios for using mathematical formulas over other methods.

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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