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

Goes well beyond the readOnly/openWorld annotations by disclosing two non-obvious behaviors: cards with no visible price return `price: null` and are deliberately retained rather than dropped, and `proxy_country` defaults to the marketplace home country so currency matches expectations. It also surfaces a cost model (one billing unit per result page) and advises keeping result volume modest, which materially affects call strategy.

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 purpose and return shape, then filters, then the detail-fetch route, then edge cases and cost — a sensible ordering. There is minor waste: "Returns JSON" repeats the opening "returns the result cards as JSON," and the billing sentence mentions `max_results`, a parameter that is not present in this tool's 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, the description usefully enumerates the returned fields and explains the null-price edge case, which is exactly what an agent needs for a 7-parameter scrape tool. The only flaw is the dangling reference to `max_results`, which does not exist in the input schema and could mislead an agent into passing an unsupported argument.

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 every parameter is already documented structurally; the description largely restates the sort options, paging, and price filters. It does add the rationale that proxy_country exists to keep currency consistent, but it introduces no new syntax or semantics for the remaining parameters.

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 ("Searches any regional Amazon marketplace for `keyword`") and immediately enumerates the returned card fields. It also distinguishes itself from the sibling detail tool by naming the `POST /marketplace/amazon-product` endpoint used to fetch full records, so an agent can tell them apart without opening either 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 clear routing guidance: use this tool for listing cards, then call the amazon-product endpoint for full detail, and use `min_price`/`max_price`/`sort`/`page` to narrow results. It does not explicitly contrast with non-Amazon siblings (ebay_search, walmart_search, google_shopping), though marketplace identity makes the choice largely self-evident.

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