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

With no annotations, the description carries the full burden. It usefully discloses cost and payment mechanics ('x402 price $0.002/call (USDC, eip155:8453)') and the computational method, which are real traits beyond the schema. However, it says nothing about error behavior for invalid inputs (negative principal, zero years) or rounding/precision of results.

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 compact segments: the computation sentence first, then the pricing detail. Every clause earns its place — inputs, outputs, and formula are packed into one sentence with no 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?

No output schema exists, but the description compensates by naming the three returned quantities and the formula used, so an agent knows what comes back. Since none of the parameters are optional and the math is deterministic, little else is needed; only edge-case handling is unaddressed.

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 schema already documents all three parameters, and this is the baseline 3 case. The description's phrasing 'annual interest rate' adds mild disambiguation of the rate unit (percent, per schema) but no format, bounds, or constraint details beyond it.

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 ('Calculate the fixed monthly payment for a loan'), names all three inputs, and enumerates the outputs (total repaid, total interest) plus the method (annuity formula). An agent can distinguish this from finance_roi_calculator or calculators_compound_interest_calculator 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?

Usage is implied by the name and the stated inputs, but there is no explicit when-to-use versus the many sibling calculators (compound interest, ROI, margin) and no exclusions or prerequisites. An agent must infer routing from the description alone.

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