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

Annotations only declare readOnlyHint and openWorldHint; the description adds real context beyond that — the data source (Keepa), the marketplace availability restriction, and the rank interpretation ('lower is better; a falling rank means rising sales'). It does not discuss latency, credits, or result size, so not a 5.

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?

Front-loaded with the core purpose, then a dense but useful metric enumeration, then usage and a constraint. The long parenthetical metric list is information-rich rather than padded, though it is somewhat crowded into one sentence.

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 carries the return-value burden and does so by enumerating price stats, rank, ratings, review counts, launch date, units bought, and a weekly trend. The only gap is that it does not note the marketplace restriction's interaction with the schema enum (au/ae remain valid inputs), which an agent might trip on.

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 100% so the baseline is 3, but the description adds interpretive meaning the schema lacks — the rank direction convention and the default window (90 days). It does not explain the marketplace codes beyond the schema's own list.

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 resource (Amazon product history over N days) with the exact metrics returned, which clearly separates it from siblings like amazon_product or amazon_listing_audit. An agent can identify it without opening the schema.

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 concrete use cases ('tell whether a competitor is growing, how they price around events, how fast they gain reviews') and a hard exclusion ('Not available for au and ae'). It does not name a competing sibling tool for adjacent needs, so it falls short of a 5.

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