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

Annotations already cover the full safety profile (readOnly, idempotent, closed-world, non-destructive), so the bar is lower. The description still adds real value by disclosing that no sign-in is required and that the call both lists examples and opens one. It does not describe what the agent receives back or how the viewer behaves, which is the remaining gap.

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 tight sentences: capability first, then the default behavior, then the intended use case. No filler; even the 'no sign-in, free' clause carries auth-relevant information for the agent.

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?

A simple read-only tool with one optional parameter and no output schema, and the description covers what it does, that it needs no auth, and when to reach for it. Only the shape of the response is unaddressed, which is minor at this complexity.

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% for the single optional model_id parameter, so baseline is 3. The description restates the default ('the first, or model_id') but adds no syntax, format, or discovery guidance beyond the schema.

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?

States a specific verb and resource: it lists example 3D models and opens one in an interactive viewer. The phrase 'made with Wandy3D' and 'example' distinguishes it in spirit from list_models, though that sibling is never named. An agent can tell what it does without opening the schema.

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?

Gives an explicit usage scenario: show what results look like before the user makes their own. It does not name a when-not condition or point to list_models as the alternative for the user's own models, so differentiation is left partly to inference.

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