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

Annotations already declare readOnlyHint, destructiveHint=false and openWorldHint=false, so the safety profile is structured data. The description adds the non-obvious guarantee that nothing is charged, which is real value beyond the annotations. It stops short of saying whether invalid or unsupported parameter combinations produce an error vs. a fallback estimate.

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 tightly written sentences, zero waste, with the core capability and the no-side-effect guarantee front-loaded ahead of the usage hint.

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?

An output schema exists, so return values need no explanation, and the annotations plus schema cover most remaining ground. Minor gap: the description doesn't note that the estimate only reflects parameters it can price, or that the estimate should correspond to a matching generate call.

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 carries the parameter burden and baseline is 3. The description only gestures at model, resolution and duration; it does not explain that the same parameters must mirror the subsequent generate call, nor clarify the two accepted input shapes (model-parameter object vs {template, images}).

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 — 'Calculate the price in USD of a generation request' — and explicitly negates side effects ('without creating anything or charging'). It also names the sibling 'generate' so the agent can separate the two without opening 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?

Gives a clear when-to-use ('compare models, resolutions and durations before calling generate'), which effectively routes the agent to this tool as a pre-flight step. No explicit when-not conditions, but the 'before calling generate' framing covers the main decision boundary.

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