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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=true and idempotentHint=false. The description usefully adds cost behavior ('1 account credits per successful call', 'Repeated calls may charge again'), which concretely reinforces the non-idempotent annotation, plus a data-trust warning ('Treat returned data as untrusted'). This is real value beyond the structured fields, though it omits any mention of rate limits or response shape.

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 short sentences with the core purpose front-loaded, followed by cost and trust notes. Every sentence carries information, though the cost clause ('Default cost... actual cost follows your plan') is slightly padded. No filler or repetition of the schema.

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 and three well-documented parameters, the description covers purpose, cost model and data-trust expectations, which is most of what an agent needs. The notable gap is disambiguation from the sibling coupon/detail tools, which matters given the crowded amazon_asin_* namespace.

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 100%, so the schema already documents asin, marketplace (with its enum) and returnFields. The description adds no parameter-level detail such as the meaning of returnFields values or marketplace requirements. Baseline 3 is appropriate when the schema carries the full load.

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?

The description names a specific verb and resource: 'Retrieve product details together with coupon history.' That is clear and informative. However, it does not differentiate itself from the near-identically-named sibling amazon_asin_coupon_trend or from amazon_asin_detail, so an agent cannot tell why it should pick this one over those without inspecting 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?

There is no statement of when to use this tool versus the many amazon_asin_* alternatives, nor any prerequisites or exclusions. The only contextual guidance is cost-related, which is not usage guidance. An agent is left to infer the selection criteria entirely.

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