Amazon FBA or FBM fees for one unit

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

Annotations already declare the safe read-only/idempotent profile, and the description adds substantial non-schema behavior: strict validation that rejects invalid/unknown arguments naming the field rather than silently adjusting, and disclosure that the response includes assumptions, fee table version/date and source URLs. This is meaningful context beyond the annotations, though error/edge behavior is not exhaustive.

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?

A single dense paragraph, but it is front-loaded with the core purpose and requirements before the fee breakdown and return details. Every clause carries information, though the length is near the upper bound for readability.

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 14 parameters with an output schema, the description covers the required inputs, dependencies, return contents and validation behavior, while annotations carry the safety profile. An agent has everything needed to invoke it correctly without opening other tools.

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% and each parameter is already documented (defaults, enums, FBA/FBM conditions), so the baseline is 3. The description mostly restates these requirements and adds only light cross-parameter semantics (peak/non-peak by ship date, apparel/dangerous fee cards) rather than details that go beyond the schema.

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 ('Calculate Amazon.com (US) fees for one unit, FBA or FBM') and then enumerates the exact fee components computed (referral, closing, per-item/subscription share, fulfillment, surcharge, storage). This is unambiguous against sibling fee tools like ebay_fees/etsy_fees (US Amazon scope) and amazon_profit (fees, not profit).

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 context: FBA requires length_in, width_in, height_in, weight_lb, and routes the agent to list_amazon_categories for category ids. It does not name alternatives to use instead (e.g., amazon_profit, compare_marketplaces) or state explicit when-not conditions, so it falls short of a 5.

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