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

Beyond the annotations, the description adds meaningful behavioral context: the free-tier/paid-call pricing via x402, exact-arithmetic computation, single rounding at the currency scale, and the final-payment adjustment so the balance ends at zero. It does not cover error behavior, but it goes well past what readOnlyHint/openWorldHint convey.

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 description is compact and front-loads the pricing note, then states outputs and rounding behavior in two sentences. It is efficient, though the bracketed pricing prefix slightly crowds the opening.

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 usefully names the returns (monthly payment, total interest, total paid). However, for a five-parameter financial calculator it leaves key required parameters and the relationship between inputs and outputs under-specified, so it is adequate but incomplete.

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 only 20%, so the description needs to compensate but largely does not. It mentions 'scale' and 'rounding' indirectly through the rounding sentence, but gives no meaning for principal, annualRatePercent, or termMonths, leaving required parameters undocumented in both schema and description.

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 resource and outputs: 'Monthly payment, total interest and total paid for a fixed-rate amortizing loan, in exact arithmetic.' That is clear enough for an agent to know what the tool computes, though it does not explicitly contrast itself with siblings such as interest_calc or money_calc.

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 only implied by the phrase 'fixed-rate amortizing loan'. There is no explicit statement of when to choose loan_calc over interest_calc, money_calc, or decimal_calc, nor any exclusions or prerequisites.

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