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

Beyond the readOnly/openWorld annotations, the description discloses real behavioral context: price is set by the IP-inferred delivery location, proxy_country defaults to the marketplace's home country, the request is routed through in-country proxies, and exitCountry is reported back. Billing behavior is also disclosed, though the "listing plugins bill one unit per result page... keep max_results modest" clause references a parameter that does not exist here and reads as copied from a search tool.

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?

The field enumeration is front-loaded and the proxy/currency explanation is well placed, but the return-field list is a long comma chain and the final billing sentence drags in an irrelevant `max_results` concept. That stray sentence is not just redundant, it actively suggests a parameter the tool lacks.

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?

There is no output schema, so the description carries the burden of describing the return shape, and it does so thoroughly (title, price, availability, features, categories, images, exitCountry). Missing only failure-mode context such as behavior when an ASIN is invalid or a page is blocked.

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?

With schema description coverage at 100%, the schema already documents all four parameters, including the proxy_country/currency rationale. The description restates the asin-or-url choice and the proxy_country default without adding format, validation, or precedence detail beyond what the schema provides, so the baseline 3 applies.

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 opening sentence names a specific verb and resource ("Fetches a single Amazon product") and enumerates the JSON fields returned, so an agent knows both what it gets and that it is a single-item lookup rather than a search. This distinguishes it from siblings like amazon_search and amazon_reviews without ambiguity.

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?

It gives a clear selection rule for inputs ("Identify the product with either `asin` (plus `marketplace`) or a full product `url`"), which is genuinely useful, but it never names an alternative sibling (amazon_search, browse_page, fetch_html) or states when not to use it. The closing sentence about "listing plugins" and "max_results" does not map to any parameter on this tool and muddies rather than clarifies usage.

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