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

Annotations already declare readOnlyHint/idempotentHint/openWorldHint, so the safety profile is covered. The description adds value beyond them: it discloses the tool is free ("FREE", "nothing is paid") — a cost trait annotations cannot express — and that it performs parameter-presence validation.

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 sentences with "FREE" front-loaded as the most decision-relevant fact, and the parenthetical clarifies the mechanism without padding. Nearly every word earns its place, though the parenthetical could be trimmed slightly.

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 should ideally indicate what a quote returns (amount, currency, validity window), and it does not. It also omits what the params object must contain, so an agent has enough to know when to call it but not quite enough to call it correctly for arbitrary products.

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 description coverage is 0% and there is a nested free-form "params" object with additionalProperties:true plus a product enum. The description says required params are checked but never explains what belongs in "params" (presumably the arguments of the corresponding product call) or how product maps to them, leaving the key parameter undocumented in both places.

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+resource: it returns the exact price of one call before paying, and explicitly clarifies it asks the API for a payment quote rather than executing anything. It implicitly contrasts with the paid sibling (call_product) but never names it, so sibling differentiation is left to inference.

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?

"before paying" gives clear timing context for when to invoke this tool, and "Also checks that required params are present" indicates a pre-flight validation role. It stops short of naming the alternative tool or stating exclusions, so it does not reach the explicit when/when-not level.

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