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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuine context beyond that: no network, no stored state, determinism, ASCII labels returned unchanged, and concrete limits (64 KB input, 1 s per call, 1 MB result). Only the limits are boilerplate-style, keeping it just short of a 5.

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 EN block is front-loaded and well-ordered: purpose, when, not-for, side effects, determinism, limits. The full ES/EN duplication doubles the length, which is a deliberate bilingual convention rather than filler, but it does cost some density.

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 single-parameter, deterministic conversion tool with rich annotations and an output schema, nothing an agent needs is missing: direction, alternative, pass-through behavior, side effects, and resource limits are all stated.

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% and the single parameter has its own description and example, so the baseline is 3. The description contributes one useful semantic detail not in the schema, that non-xn-- ASCII labels pass through unchanged, but adds no format guidance beyond that.

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 ('Convierte etiquetas Punycode xn-- de un dominio a Unicode (RFC 3492)') and immediately distinguishes itself from the sibling 'punycode-encode'. An agent can pick the right direction of conversion 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?

Explicitly names the exclusion and the alternative ('No para: convertir un dominio internacionalizado a ASCII (punycode-encode)'). The 'Cuándo' clause is somewhat generic and the 'to or from this encoding' phrasing blurs directionality slightly, but the routing guidance is unambiguous.

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