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

Annotations already cover readOnly/idempotent/non-destructive, but the description adds non-obvious context: 'Free discovery endpoint: it does not charge credits' — a cost trait annotations cannot express. It also enumerates what the response contains (id, label, description, family, pixel art flag, thumbnail_url, version, settings, advanced_settings), compensating for the absent output schema.

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?

Purpose and the free-endpoint/ordering guidance lead; the schema of returned fields is listed densely in the middle. Every clause carries information, but the single long sentence listing seven response fields is heavy and could be tabulated or trimmed.

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?

No output schema exists, and the description fully documents the return shape including nested setting objects and advanced_settings, plus cost and sequencing. An agent can call it and use the result with no gaps.

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?

Zero parameters, so baseline is 4. The description goes slightly further by explaining downstream semantics (the id is passed as style_id; a setting's name is the key in style_params), which helps the agent chain calls, though this is arguably usage rather than parameter info.

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 ('List the styles Directional Sprites can render a 3D model in') plus scope ('perspectives (camera heights)' and 'eight directions'). Clearly distinguishable from creation siblings like createDirectionalSprites and previewDirectionalSprites.

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?

Explicitly instructs 'Use it before previewDirectionalSprites, createDirectionalSprites and createDirectionalStills', naming the three alternatives and the ordering condition. No inference required.

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