set_calculated_property

Set a property value using a Lua expression based on its current value

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.

HTTP Endpoint

POST /tools/set_calculated_property

Parameters

path · string · required

The path to the instance (e.g., “game.Workspace.Part”)

property · string · required

The name of the property to set

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.

Response

ok · boolean

Returns true if the property was successfully set

newValue · any

The new value that was set, serialized to JSON format

error · string

Error message if the operation failed (path not found, property doesn’t exist, expression error, etc.)

Code Examples

Double a numeric value

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

Increment a number

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

Conditional transformation

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

String manipulation

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

Math operations

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

Clamp a value

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

Example Response

Success

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

Expression error

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

Evaluation error

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

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