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

Annotations already declare readOnlyHint, openWorldHint, non-idempotent and non-destructive. The description usefully adds credit cost per call, that repeated calls may charge again (reinforcing the non-idempotent hint), and a data-trust warning — real behavioral context beyond the structured fields.

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, purpose front-loaded before the cost and trust caveats. Every sentence carries information; only minor tightening would be possible.

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 hint at what 'research metrics' are returned (volume, rank, trend series?), but it does not, and the mismatch between the 'trends' name and 'historical research metrics' phrasing is unresolved. Cost and trust info partially compensate.

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 are fully documented in the schema. The description adds no syntax, format, or default guidance for keyword, marketplace, month, or returnFields, so baseline 3 is appropriate.

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 (Retrieve) and resource (historical research metrics for a keyword), so the agent knows the general operation. However, it does not differentiate from the very similarly named sibling amazon_keyword_research or from amazon_aba_research_trends, leaving the 'trends' aspect undefined.

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?

No when-to-use guidance, no exclusions, and no named alternatives, despite there being several closely related keyword sibling tools (amazon_keyword_research, amazon_keyword_miner, amazon_aba_research_trends). The agent must guess which keyword tool applies.

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