Create a new instance in the Roblox DataModel to add parts, scripts, or folders. Specify class name, parent, and initial properties.
Creates a new Instance in the DataModel
| Name | Required | Description | Default |
|---|---|---|---|
| name | No | Name for the new instance | |
| parent | No | Parent path (e.g. 'game.Workspace') | game.Workspace |
| className | Yes | Class name of the instance (e.g. 'Part', 'Folder', 'Script') | |
| properties | No | Key-value dictionary of initial properties |
Changes observed during successful MCP inspections.
v1.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations are absent, so the description carries the full behavioral burden, and it discloses very little. It does not say whether the instance is immediately visible in the tree, what happens if the className is invalid or the parent path does not exist, or whether the call requires specific permissions. 'Creates' is the only behavioral signal given.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
A single short sentence with no filler, and the verb/resource lead is front-loaded. It is efficient, though its brevity reflects under-specification rather than disciplined concision.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a mutation tool with no annotations, no output schema, and a nested 'properties' object, the description is too thin. It omits failure modes, return value, and whether the newly created instance is auto-parented when 'parent' is defaulted, leaving meaningful gaps for an agent invoking a state-changing operation.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100% (name, parent with default 'game.Workspace', className with examples, properties dictionary), so the schema already documents all four parameters. The description adds no parameter detail at all, making the baseline 3 appropriate rather than a penalty.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description uses a specific verb+resource ('Creates a new Instance in the DataModel') that clearly distinguishes this write tool from siblings like get_tree, delete_instance, and read_script. It does not, however, name or differentiate against execute_luau, which can also instantiate objects, so it stops short of full sibling disambiguation.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
No when-to-use guidance is provided. It never states prerequisites (e.g. a valid parent must exist), nor does it mention that execute_luau is an alternative for instance creation. The agent is left to infer all routing logic from the one-line purpose.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.