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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so 'sin efectos secundarios, solo lectura' is largely a restatement. The description does add value beyond them: the Excel cash-out-negative sign convention, end/begin payment timing, determinism, and hard limits (64 KB input, 1 s per call, 1 MB result).

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 structure is strongly front-loaded — purpose, then Cuándo / No para / Efectos / Determinista / Límites — which is easy to scan. It loses a point for shipping the same content twice (Spanish block then English block), which inflates length without adding information.

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 an output schema present and rich annotations, the description only needed to cover preconditions and call semantics, and it does: limits, determinism, sign convention, and the loan-payment exclusion. What remains thin is what happens on inconsistent inputs (which variable wins, error shape) — a minor gap given the existing annotations and output schema.

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 coverage is 100%, so the baseline is 3, but the description adds genuine semantics the schema does not: the Excel sign convention for cash flows and the fact that rate/payments are per period, which materially affect how pv/fv/pmt values must be signed. It stops short of explaining solver failure behavior when inputs are inconsistent.

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?

It names a specific verb and resource — solving for the one missing TVM variable — and enumerates the exact variables (pv, fv, pmt, nper, rate) plus the sign convention. It also explicitly names the sibling it is not (fin-loan-payment), so the agent can separate the two without opening either 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?

The 'Cuándo' clause gives a positive trigger (money/tax/financial-math results that must be exact and reproducible) and the 'No para' clause gives an explicit exclusion routing to fin-loan-payment for amortizing-loan payments. Both when-to-use and when-not-to-use are stated, with the alternative named.

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