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

Annotations already establish readOnlyHint=true, destructiveHint=false, and idempotentHint=false. The description adds genuinely useful context beyond them: per-call credit cost, the possibility of repeat charges on repeated calls (reinforcing non-idempotency), and an explicit instruction to treat returned data as untrusted. The billing and trust details are the value-add here.

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, front-loaded with the core purpose before billing and safety notes. Every sentence carries information, though the two cost sentences could be tightened into one.

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?

For a four-parameter estimate tool with no output schema, the description covers purpose, cost, and trust but omits any indication of what the estimate returns or how it relates to the ASIN-based sibling. Adequate but with a clear differentiation gap.

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 all four parameters including the marketplace enum and returnFields are already documented in the schema. The description only loosely maps 'category and BSR rank' to two of the required inputs and adds no format or syntax detail, so it meets the baseline without exceeding it.

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: 'Estimate product sales from category and BSR rank,' which is concrete and actionable. It fails to distinguish itself from the sibling amazon_sales_prediction_asin, which is the closest alternative and differs only in input basis (BSR vs ASIN).

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 guidance on when to use this tool versus amazon_sales_prediction_asin or amazon_asin_sales_trend. The only conditional content concerns billing ('Repeated calls may charge again'), which is cost guidance rather than usage routing.

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