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

Annotations already cover safety (readOnlyHint) and open-world scope, so the bar is lower. The description still adds real value beyond them by disclosing the 3-credit cost and clarifying that the data is public and includes an inline review sample. It omits caching semantics, which matters given the cache_max_age parameter.

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?

Two short sentences, front-loaded with the resource and return fields, with the cost appended as a discrete operational note. Nothing is redundant with the name or title.

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 read-only lookup with no output schema, listing the returned fields is genuinely useful and covers the main information need. The gap is the undescribed cache_max_age parameter and the absence of any note on failure modes for invalid ASINs or unavailable marketplaces.

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 75%, with asin and tld well documented in the schema, so the baseline is 3. The description adds no parameter-level meaning at all — nothing about how the marketplace TLD interacts with country_code, and nothing at all about cache_max_age, which the schema leaves undescribed.

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 (retrieves) and resource (one Amazon listing) and enumerates exactly what is returned: title, brand, price, availability, rating, specifications, review sample. The phrase 'one Amazon listing' implicitly separates it from search-style siblings, but it never names amazon_search or amazon_offers to make the distinction explicit.

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?

Usage is only implied: the required ASIN signals this is a lookup-by-identifier tool rather than a discovery tool, and the credit cost gives a rough sense of expense. There is no explicit when-to-use guidance and no statement of when to prefer amazon_offers or amazon_search instead.

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