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Description

Sets a property value by evaluating a Lua expression that has access to the current property value. This is useful for transformations, calculations, or conditional updates based on the existing value.

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HTTP Endpoint

POST /tools/set_calculated_property

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Parameters

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path
string
required
The path to the instance (e.g., “game.Workspace.Part”)
​
property
string
required
The name of the property to set
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expression
string
required
A Lua expression that will be evaluated. The current property value is available as current. The result of the expression becomes the new value.

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Response

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ok
boolean
Returns true if the property was successfully set
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newValue
any
The new value that was set, serialized to JSON format
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error
string
Error message if the operation failed (path not found, property doesn’t exist, expression error, etc.)

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Code Examples

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Double a numeric value

{
  "path": "game.Workspace.Part",
  "property": "Transparency",
  "expression": "current * 2"
}

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Increment a number

{
  "path": "game.Workspace.Counter",
  "property": "Value",
  "expression": "current + 1"
}

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Conditional transformation

{
  "path": "game.Workspace.Part",
  "property": "Transparency",
  "expression": "current > 0.5 and 1 or 0"
}

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String manipulation

{
  "path": "game.Workspace.Part",
  "property": "Name",
  "expression": "current .. '_copy'"
}

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Math operations

{
  "path": "game.Workspace.Part",
  "property": "Size",
  "expression": "Vector3.new(current.X * 2, current.Y, current.Z * 2)"
}

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Clamp a value

{
  "path": "game.Workspace.Part",
  "property": "Transparency",
  "expression": "math.clamp(current + 0.1, 0, 1)"
}

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Example Response

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Success

{
  "ok": true,
  "newValue": 0.8
}

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Expression error

{
  "error": "Expression error: [string \"return current *\"]:1: unexpected symbol near '<eof>'"
}

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Evaluation error

{
  "error": "Evaluation error: attempt to perform arithmetic on a string value"
}

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Notes

  • The expression must be a valid Lua expression that returns a value
  • The current property value is available as the current variable
  • You have access to standard Lua functions like math.clamp, math.min, math.max, etc.
  • You can construct new Roblox data types like Vector3.new(), Color3.new(), etc.
  • The expression is evaluated in a sandboxed environment for security

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