set_colorAssign a flat RGB color to a body for visual distinction before rendering, creating or reusing a design-local appearance to identify parts clearly.
Assign a flat RGB color to a body (creates/reuses a design-local appearance). Useful for visually distinguishing parts before render_view.
| Name | Required | Description | Default |
|---|---|---|---|
| red | Yes | ||
| blue | Yes | ||
| green | Yes | ||
| opacity | No | 1.0 = opaque, 0.0 = invisible | |
| body_name | Yes | Body name |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate this is a mutating, idempotent, non-destructive operation. The description adds valuable behavior beyond that by explaining that it creates or reuses a design-local appearance, which clarifies the side effect on the model and that this is not a global material change.
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?
The description is two short sentences with no filler. The core action is front-loaded, and the parenthetical adds meaningful behavioral context without bloating the text.
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 simple setter tool with no output schema, the description covers the purpose, the scoping of the appearance, and the intended rendering relationship. It does not explain the return value or mention opacity in prose, but the schema supplies the latter and the operation is simple enough that the absence is not critical.
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?
With schema description coverage at only 40%, the description partially compensates by explaining the high-level meaning of 'RGB color' and 'body', and by adding the design-local nuance. However, it does not mention the optional opacity parameter or the RGB channel ranges, although the schema does provide ranges and an opacity description.
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 opens with a specific verb and resource: 'Assign a flat RGB color to a body', which clearly identifies the operation. It also adds useful scoping ('design-local appearance') and a mention of rendering, but it does not explicitly distinguish itself from the closely related sibling set_appearance.
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?
The phrase 'Useful for visually distinguishing parts before render_view' gives a clear intended use case and temporal context. It does not explicitly state when not to use this tool or mention alternatives such as set_appearance, so it stops short of full exclusionary guidance.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.