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

Beyond the readOnlyHint/destructiveHint annotations, the description discloses non-obvious behaviors: it is 'Pure data fetch (no AI analysis)', fetches nothing and returns "MARKETPLACE NEEDED" without a marketplace, and imposes a mandatory output contract for 'Account notice:' paragraphs. This is exactly the kind of behavioral context annotations cannot convey.

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?

Every sentence earns its place: purpose, sibling routing, failure mode, output contract, and marketplace protocol are all load-bearing. However, it is a single dense wall of text with an embedded enumeration; bulleted structure would improve scannability for an agent, and some marketplace content duplicates the schema's parameter description.

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 3-parameter tool with no output schema, the description is remarkably complete: it enumerates the returned data categories, explains the marketplace failure case, the currency semantics, and the mandatory account-notice output contract. An agent has everything needed to invoke it correctly and handle unusual responses, with only trivial gaps (e.g., invalid-ASIN behavior).

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% and the schema already documents all three parameters thoroughly, so the baseline is 3. The description adds real strategic value beyond the schema by recommending the tool be called first without `sections` and by explaining how to interpret section data (e.g., 'many FBA offers means price competition') — though some marketplace guidance in the description repeats the schema text.

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+resource ('buy box, competing offers and price/rank statistics for one Amazon ASIN') and enumerates the exact data categories returned. It also differentiates from the closest sibling by stating it is 'not private-label research — for demand and revenue estimates use analyzeProduct instead', so an agent can route correctly without opening schemas.

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?

Explicitly names when to use this tool ('Built for reseller / online-arbitrage questions') and the alternative for other cases ('use analyzeProduct instead'). It also gives a concrete invocation protocol (call first WITHOUT sections, only request sections when the summary is insufficient) and tells the agent to ask once for marketplace rather than assuming the US.

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