Calculate resale selling fee, net profit, ROI, and break-even sale price. Results are rounded to two decimals; ROI is null for zero purchase price and break-even is null when the fee is at least 100 percent.
| Name | Required | Description | Default |
|---|---|---|---|
| sale_price | Yes | ||
| shipping_cost | No | ||
| purchase_price | Yes | ||
| selling_fee_percent | No |
| Name | Required | Description | Default |
|---|---|---|---|
| net_profit | Yes | ||
| roi_percent | Yes | ||
| selling_fee | Yes | ||
| break_even_sale_price | Yes |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations only give safety/idempotency hints, so the description adds real value with non-obvious behavioral rules: results are rounded to two decimals, ROI is null for a zero purchase price, and break-even is null when the fee is >= 100 percent. These edge conditions are precisely the kind of detail an agent needs to interpret output correctly.
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?
Two tight sentences: purpose first, edge-case behavior second. No filler, no redundancy, and the most decision-relevant information is front-loaded.
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?
An output schema exists, so return values need not be described, and the null/rounding rules cover the trickiest interpretation cases. The remaining gap is the thin parameter semantics for an all-undocumented 4-param schema, which keeps this just short of complete.
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 0%, so the description carries the full burden, and it does so only partially. It mentions purchase price (via the zero-price ROI rule) and selling fee (via the 100 percent break-even rule), but says nothing about shipping_cost, units/format for selling_fee_percent (e.g. 13 vs 0.13), or the defaults on the optional params.
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 (Calculate) and enumerates the exact outputs: resale selling fee, net profit, ROI, break-even sale price. An agent immediately knows what the tool returns without opening the schema, and there are no siblings to disambiguate from.
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?
Usage is implied by the name and the enumerated outputs — this is plainly a pricing/ROI calculator — but the description never states when to reach for it versus doing the arithmetic elsewhere, nor any prerequisites. With no siblings, no alternatives can be named, so 3 is the ceiling for implied-only guidance.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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