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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description still adds value beyond that: determinism guarantee, no network, no stored state, and concrete limits (64 KB input, 1 s per call, 1 MB result). It does not describe the return shape, but an output schema exists.

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?

Content is front-loaded with the formula and the when/not-for routing first, and every clause carries information. It loses a point because the entire block is duplicated in Spanish and English, roughly doubling length without adding new semantics.

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?

For a 3-parameter pure-computation tool with full schema coverage, an output schema, and complete annotations, the description covers purpose, routing, determinism, side effects and operational limits. Nothing an agent needs to call it correctly is missing.

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 real meaning: it explains that annualized ROI is produced only when a holding period in years is supplied, which clarifies the role of the optional `years` parameter beyond its schema text.

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 ("Calcula el retorno sobre la inversión (ROI) y ROI anualizado") and even gives the formula ROI = (gain − cost) / cost, so the computation is unambiguous. It explicitly names the sibling it is not (fin-cagr) and the distinction (CAGR between two values).

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?

Has explicit "Cuándo/When" and "No para/Not for" clauses, and the exclusion names the alternative tool fin-cagr with the condition that selects it. An agent can route between fin-roi and fin-cagr without opening either schema.

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