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 safety profile is covered; the description still adds real context: no network, no stored state, determinism, ±1-2 min accuracy, and hard limits (64 KB input, 1 s, 1 MB result). Minor redundancy in restating 'solo lectura' keeps it from 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 labeled structure (Cuándo / No para / Efectos / Límites) is well front-loaded, but the entire content is duplicated verbatim in Spanish and English, effectively doubling length without adding information. Every sentence earns its place individually, yet half of them are repeats.

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 described; the description still covers computations, accuracy, limits and exclusions, which is enough for a 4-parameter read-only tool. The lone soft spot is the 'Cuando' framing, which implies exactness for a tool that is itself approximate (±1-2 min).

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 each parameter (date, latitude, longitude, timezone with default UTC) is documented in the schema itself. The description only gestures at 'a latitude/longitude and date' and 'a chosen time zone', adding no syntax or format detail 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 precise verb+resource set (sunrise, sunset, solar noon, civil twilight, day length) with the inputs (latitude/longitude, date) and an accuracy bound (±1-2 min). It also names the sibling it is not for (julian-day), so an agent can distinguish it without opening schemas.

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' section gives the triggering condition (date/time-zone/calendar results that must be exact: DST, month ends, leap years) and an explicit 'No para' exclusion pointing at julian-day. Both when-to-use and when-not-to-use are covered.

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