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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so restating 'sin efectos secundarios' earns nothing. The description does add real context beyond annotations: CLDR-sourced names, 249 codes, determinism, and explicit limits (1 s per call, 1 MB result). The 'JSON input up to 64 KB' limit is suspicious boilerplate since the tool takes a string query, which slightly muddies the picture.

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 content is front-loaded and useful, but the same text is delivered twice (full Spanish block then full English block) plus a self-referential pointer to 'inputSchema.description'. That duplication roughly doubles length without adding information, and the structured-data 'Cuándo' sentence is 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?

An output schema exists, so return values need not be explained, yet the description still names them (code, both names, flag emoji). Coverage of source data, cardinality, matching rules, side effects and limits is sufficient for an agent to call this correctly on the first try.

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 baseline is 3, but the description adds matching semantics the schema does not state: accent-insensitivity, partial matching, and that names are accepted in Spanish or English. It says nothing about the `limit` parameter's behavior (truncation vs. ranked results), which is the one remaining gap.

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 (look up ISO 3166-1 alpha-2 countries) plus the lookup key modes (code, Spanish/English name, accent-insensitive, partial match) and the returned fields. It explicitly separates itself from the sibling iso-language-lookup, so an agent can pick the right tool 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 'No para' clause names the alternative (iso-language-lookup) and the exact condition that selects it, which is strong routing guidance. The 'Cuándo' clause, however, is generic boilerplate about transforming/comparing structured data and does not describe a concrete country-lookup scenario, so the positive case is weaker than the negative one.

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