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 'solo lectura, sin red, sin estado guardado' line largely restates them. However, the description adds genuinely new operational context: the 100k population floor, accent-insensitive matching, Spanish exonyms, most-populous-first ordering, and concrete limits (64 KB input, 1 s/call, 1 MB result). A contradiction check finds nothing — 'sin red' is consistent with openWorldHint=false.

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?

Well structured with labeled sections (Cuándo / No para / Efectos / Límites) and front-loaded purpose. The bilingual duplication and the repeated return-field list across the description and inputSchema.description are mild redundancy, but every block carries actionable 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, annotations covering the safety profile, and 100% parameter coverage in the schema, the description fills the remaining gaps (matching behavior, ordering, homonym handling, limits). Nothing needed to invoke this tool 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 description coverage is 100% and the schema already spells out the 'name, country' trailing-comma disambiguation trick, the limit default/bounds, and that country accepts ISO code or name. The description adds only the accent-insensitivity and Spanish-exonym note, so it sits at the baseline where the schema does the heavy lifting.

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?

A specific verb plus resource (look up cities ≥100k inhabitants by name) with the exact return fields enumerated (country, population, coordinates, IANA zone, GeoNames ID) and homonym flagging. This is clearly distinct from siblings like city-distance and city-local-time, which the description explicitly separates.

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 'Cuándo' block names the exact triggering conditions (resolving a city name to country/coords/population/time zone, disambiguating homonyms), and the 'No para' block routes the agent away to city-distance for great-circle distance. When-to-use, when-not, and the alternative are all explicit.

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