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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description reinforces this with 'Read-only' (slightly redundant). It adds genuine context beyond the annotations: the fees come from the official Amazon Product Fees API, and net_proceeds is explicitly before cost of goods. It does not cover rate limits or auth needs, but the safety profile is well covered.

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 purpose and API, then inputs, then return values, then the margin use case. Dense but every sentence carries useful information; the one redundancy is restating 'Read-only' that the annotations already establish.

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 properly enumerates the returned fields (referral_fee, fba_fee, closing_fee, total_fees, net_proceeds) and clarifies the semantics of net_proceeds. The only incompleteness is the unaddressed account_id parameter.

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 only 50%, so the description must compensate. It explains the asin-OR-sku choice, the price/currency inputs, and that fulfillment_channel defaults to FBA with FBM as the alternative, adding meaning beyond the schema. The account_id parameter is left unexplained in the description (its only description is in Italian in the schema), which is the main gap.

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 ('Estimate Amazon fees... and net proceeds for a given selling price') and names the exact underlying API (getMyFeesEstimate). Fee estimation is unique among the siblings, so the agent can distinguish it immediately without opening the schema.

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 a clear use case ('Use it for real margins: margin = net_proceeds - purchase cost') and the input condition ('Pass asin OR sku'). However, it does not name an alternative sibling or state when NOT to use it, so routing guidance is implied rather than explicit.

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