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

Annotations already declare readOnlyHint, openWorldHint=false, idempotentHint and destructiveHint=false, so the safety profile is covered; the description's 'solo lectura, sin red, sin estado guardado' largely restates them. It does earn its keep with genuinely new facts: determinism, hard limits (64 KB input, 1 s, 1 MB result) and the CLDR-vs-ISO caveat (COP shows 0 decimals), which affects rounding behavior.

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?

Front-loaded with the core statement, then clearly labeled sections (Cuándo / No para / Efectos secundarios / Determinista / Límites), which is easy to scan. It loses a point for the bilingual duplication and the awkward meta-reference to 'inputSchema.description' instead of closing the English sentence in place.

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, the description need not describe return values, and everything else an agent needs is covered: what the tool returns, when to use it, the alternative, side effects, determinism and operational limits. Nothing material 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, and the description goes past it by explaining that the symbol/narrow symbol is locale-dependent while names are fixed in English and Spanish, which clarifies the scope of the optional locale parameter. It still leaves the locale default/pattern and the code pattern to the schema, so not a 5.

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 ('Devuelve los datos de una moneda ISO 4217') and enumerates exactly what is returned: decimales, símbolo y nombre en inglés y español, plus an explicit exclusion ('Sin tasas de cambio'). It also names the distinct sibling it is not (currency-format), so an 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?

Uses explicit 'Cuándo:' and 'No para:' framing: use it when money/tax/financial math must be exact and reproducible, and do not use it for locale/país amount formatting (currency-format). Positive trigger and named alternative with the selecting condition are both present.

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