eBay break-even and target-margin price

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

Annotations already declare readOnly/idempotent/non-destructive and closed-world, so the safety bar is low. The description adds real behavioral context beyond that: strict input validation with field-naming rejection messages and no silent adjustment, plus it names the shared fee engine and the fee-table versioning. It stops short of documenting pagination or failure modes, but the validation contract is genuinely useful.

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?

The core purpose is front-loaded in the first clause, and each following sentence carries distinct information (fee-step handling, unit conventions, fee engine, return contents, validation). It is dense at six sentences but nearly all of them earn their place; the return-contents sentence is somewhat redundant given the 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?

For a 12-parameter computation tool with full schema coverage, an output schema, and safety annotations, the description supplies the remaining essentials: unit conventions, fee-step handling, and the strict-validation contract. It does not explain the return shape, but the output schema already covers that, so nothing critical is missing.

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%, so the baseline is 3. The description does add unit meaning (percent inputs like '8.25 means 8.25%'), but its claim that 'Money is in whole cents' sits awkwardly against the schema's per-parameter 'USD' wording and multipleOf 0.01, which could mislead rather than clarify. Net value over the schema is marginal.

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?

Starts with a specific verb and resource — 'Find the lowest eBay.com (US) item price that breaks even and the lowest that reaches target_margin_pct' — which precisely describes the inverse-pricing computation. This is clearly distinguishable from sibling ebay_profit (which computes profit at a known price) without opening either schema, even though that sibling is not named.

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?

The description defines the scenario ('breaks even / reaches target_margin_pct') which implies when to reach for this tool, but it never explicitly routes the agent between this and the siblings ebay_profit, etsy_target_price, or amazon_target_price, nor states when-not to use it. Usage is inferable but not spelled out.

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