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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description usefully adds what is actually computed and returned (fee, APR, renewal cost), which matters because there is no output schema. It does not describe edge-case behavior such as what happens with zero renewals or missing fee_per_100.

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 purpose and the outputs are front-loaded in the first sentence, and the second sentence supplies concrete usage triggers. The opening enumeration of loan types is a bit list-heavy, but no sentence is filler.

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 carries the burden of naming return values, and it does name three (fee, APR, renewal cost). All five parameters are fully described in the schema. What remains missing is any note on result units or edge cases, which is a minor gap for a pure calculator.

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 every parameter is already documented in the schema, and the baseline is 3. The description reinforces the fee-per-$100 and rollover semantics through its examples but adds no format or boundary detail beyond what the schema states.

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?

The description states a specific computation and its outputs: 'the fee in dollars, the APR, and what renewing (rolling over) costs'. It also scopes the applicable instrument class ('payday loan, title loan, pawn loan, cash-advance app or any loan priced by a fee for a number of days'), which separates it from amortized-loan siblings like loan_payment and average_loan_rates without needing their schemas.

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 gives a clear inclusion condition ('any loan priced by a fee for a number of days') and two concrete triggering questions about APR and rollover cost. It stops short of naming an alternative or stating when NOT to use it, so an agent must infer the boundary against loan_payment on its own.

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