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

Annotations already declare readOnlyHint, destructiveHint=false, idempotentHint and openWorldHint=false, so the description doesn't need to restate safety basics. It still adds value the annotations cannot express: no network access, no stored state, determinism guarantee, and hard operational limits (64 KB input, 1 s per call, 1 MB result). Minor redundancy with openWorldHint but the limits are genuinely additive.

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 and front-loaded: purpose first, then When / Not for / Side effects / Deterministic / Limits as scannable labelled clauses. It loses a point because the Spanish and English blocks convey the same content, roughly doubling length, plus a truncated pointer clause ('[EN completo / full EN: inputSchema.description]') that adds no 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?

An output schema exists, so return values need no prose, and everything else an agent needs is present: purpose, trigger conditions, the excluded sibling, side effects, determinism and resource limits. Nothing required to call this 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 both parameters carry their own descriptions including the 'at' default of 2026-01-01T00:00:00Z, so the baseline is 3. The description clarifies conceptually that offsets/names are computed *at* that instant, but adds no syntax hints (acceptable IANA formats beyond the example, ISO-8601 shape for 'at') beyond the schema.

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?

Names a specific resource (a time zone at a given instant) and enumerates exactly what is reported: UTC offset, local time, January/July offsets, DST flag, short and long names. It also explicitly rules out the nearest sibling, timezone-list, so the agent never confuses the lookup tool with the data tool.

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?

Gives a concrete 'When' trigger (a date, time-zone or calendar result that must be exact: offsets, DST, month ends, leap years) and a concrete 'Not for' exclusion naming the alternative tool (timezone-list). Both the positive and negative routing conditions are stated, leaving nothing to inference.

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