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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds value beyond them by stating the call is free ('Costs nothing'), that it returns credits at a stated conversion (1 credit = $0.01), the model that would run, and a breakdown. The 'Pass the same input' contract is also a behavioral rule not captured by annotations.

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?

Three tight sentences, front-loaded with the core action and the 'WITHOUT running it' distinction in the first line, followed by return shape and then usage triggers. No filler.

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?

With no output schema, the description supplies the return contents (credits, model, breakdown) that would otherwise be unknown. It also covers cost and the input-passthrough contract, so an agent has everything needed for a 2-param preview tool.

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 50%, with the `kind` enum and the `input` object already described structurally. The description reinforces the key semantic constraint that `input` must be exactly the arguments you would pass to generate_<kind>, and semantically ties kind to the corresponding sibling tool, which is meaningful 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 (price) and resource (a generate_* call) and explicitly distinguishes itself from the sibling generate_image/generate_video/generate_audio tools by saying it runs nothing. An agent can tell instantly what it does and what it does not do.

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 explicit trigger conditions: before spending when the user asks about cost, when choosing between models, or before a clip longer than a few seconds. It also names the alternative behavior implicitly (call generate_* directly to actually run), leaving nothing to inference.

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