draw_ellipsoid

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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=false, so the safety profile is covered; the description adds the meaningful 'what gets replaced' detail ('add' fills with color replacing voxels there, 'paint' recolors only existing voxels, 'carve' removes them). The carve wording ('removes the part's voxels') sits in mild tension with destructiveHint=false, though the undo sibling makes the edit reversible, so it reads as clarification rather than contradiction. No pagination/return-format concerns apply for a modeling op.

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?

Two short, front-loaded blocks: a purpose sentence followed by a single worked example, with no filler. It loses a point only because the example's meter-to-voxel mismatch adds a small ambiguity rather than clarity.

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 drawing primitive with full schema coverage and no output schema, the description plus schema covers everything needed to invoke it: the shape definition, the three modes, the color requirement and a placement example. Nothing essential to correct invocation is missing.

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 coverage is 100%, so the schema already documents center, radii, mode, color, part and project, and the baseline is 3. The description contributes the inclusion rule ('voxel centers inside the surface') and ties center/radii together in the example, but the example itself is ambiguous because it mixes meters ('1.2 m wide') with voxel radii [6, 4, 10] without explaining the scale factor.

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 names three concrete operations (add, paint, carve) on a specific resource (ellipsoid or sphere) and defines the geometry rule ('voxel centers inside the surface'). This clearly separates it from siblings draw_box, draw_cylinder and draw_wedge without opening their schemas.

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?

Mode semantics (add/paint/carve) are stated, and the dome-on-a-roof example gives concrete placement context, but the details of each mode live in the schema, not the description. There is no explicit statement of when to pick an ellipsoid over draw_box/draw_cylinder, nor prerequisites such as the part already existing or needing define_color first.

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