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

Annotations already declare readOnly/openWorld/non-idempotent. The description adds valuable non-obvious behavior: each product is 'filled in from its product page' (i.e., an extra fetch per item) and the cap of 20 per call. It does not mention rate limits or latency, but the enrichment cost is disclosed.

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 action, then limits, then the returned field list. Dense but every clause carries information; the field enumeration is long but justified given no output 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 normalized product fields and notes per-item page enrichment. Minor gaps remain (e.g., no note on failure/empty results or language/store caveats), but it is sufficient to invoke correctly.

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 itself documents limit clamping (larger lowered to 20, 0/negative → default) and the query example. The description only restates 'Body: {query, limit}', adding nothing beyond the schema, so 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?

States a specific verb+resource+scope: 'Keyword search on Amazon.com (US store)', with per-call limits. This clearly distinguishes it from the amazon-reviews sibling and other search siblings.

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?

'Good for price checks and product comparison' gives concrete usage context, and the store scoping (US) implicitly rules out other locales. No explicit when-not or named alternative, but the intended use case is clear.

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