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add_part

Create an empty named part in a .vox model's body, then fill it with draw tools; use separate parts for distinct XML objects.

Instructions

Add an empty part to the body (one named object in the .vox file).

Use one part for the main body; separate parts only for pieces that are separate objects in the XML. Draw into it with the draw_* tools; its size follows its voxels.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "project": "<project>",
      "name": "<name>"
    },
    "name": "add_part"
  }
}

Input Schema

Name	Required	Description	Default
`name`	Yes	Part name, for example 'body' or 'wheel_fl'.
`project`	Yes	Project name, for example 'red_pickup'.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.4.0Oct 7, 2026

TDQS

A3.9/5.0

Behavior4/5

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

Annotations declare non-read-only, non-destructive, closed-world, so the safety profile is covered. The description adds real behavioral context beyond that: the new part starts empty and 'its size follows its voxels,' which tells the agent the part is defined implicitly by drawn geometry.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the core action, followed by usage rule and next-step pointer. No filler; the parenthetical definition is valuable rather than redundant.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a two-parameter, no-output-schema creation tool, the description covers what is created, when to create one, and what to do next. It could state how the newly created part is referenced by the draw_* tools, but that gap is minor.

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?

Schema description coverage is 100%, with both 'name' and 'project' documented and exemplified in the schema, so baseline is 3. The description adds only a conceptual gloss ('one named object'), not new parameter syntax or constraints.

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?

States a specific verb and resource ('Add an empty part to the body') and clarifies the domain concept as 'one named object in the .vox file.' It is clearly distinguishable from siblings like remove_part, though it does not name the inverse operation explicitly.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives concrete when-to-use guidance ('Use one part for the main body; separate parts only for pieces that are separate objects in the XML') and routes the agent to the next step ('Draw into it with the draw_* tools'). It lacks an explicit when-not-to-use or a direct pointer to a named alternative.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.