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

Adds real value beyond the annotations: the non-determinism rule ("según el reloj salvo que se dé at") tells the agent how to get reproducible output, and the stated limits (64 KB input, 1 s per call, 1 MB result) are not in any structured field. The "sin red / sin estado guardado / solo lectura" line largely restates readOnlyHint and openWorldHint, so not everything is net-new.

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 scoping constraints, limits, and exclusion are front-loaded, which is good. But the content is effectively duplicated in Spanish and English, and the trailing artifact "[EN completo / full EN: inputSchema.description]" is a placeholder that consumes space without conveying 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, return values need no explanation, and the annotations already carry the safety profile. The description still covers the pieces an agent needs to call it correctly: default timezone, the deterministic override, the DST/exactness use case, and the sibling exclusion.

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 description coverage is 100%, so the baseline is 3. The description only echoes the schema-level idea that a value for `at` can be supplied "para pruebas"; it adds no format, default, or precedence detail (e.g. naive local time interpreted in `timezone`) that the schema does not already carry.

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 concrete verb+resource ("Devuelve el instante actual ... en una zona horaria IANA") and enumerates the exact fields returned. It also names the sibling it is not (timezone-shift), so an agent can separate it from the other timezone tools without opening a 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?

Explicit "Cuándo" condition (dates/time zones/calendars that must be exact: offsets, DST, month ends, leap years) and an explicit "No para" exclusion that routes conversion work to timezone-shift. Both when-to-use and when-not-to-use are given, 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.