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

Annotations already declare read-only, idempotent, non-destructive and closed-world, and the description still adds substantive context: no network, no stored state, determinism, hard limits (64 KB input, 1 s per call, 1 MB result), and sub-millimetre in-zone accuracy with the Norway/Svalbard zone exceptions called out. That is more than the annotations provide and is exactly the kind of behavioral detail an agent needs.

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 English block is dense, front-loaded (purpose first, then when/not-for, then effects and limits) and every clause carries information. The cost is that the entire text is duplicated verbatim in Spanish, so roughly half the characters add nothing for a single-language reader.

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-value explanation is unnecessary, and the description still covers accuracy, edge-case zone rules, determinism and resource limits. The only meaningful omission is the `zone` input override, which the description mentions only as an output concept.

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%, so lat and lon are fully documented by the schema and the description correctly implies their meaning. However, the optional `zone` override — the one non-obvious parameter — is never mentioned in the description, so no value is added beyond structured data. Baseline 3 applies.

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 (convert WGS84 lat/lon to UTM zone, band, hemisphere, easting, northing) and even names the projection method and the Norway/Svalbard exceptions. The negative clause explicitly distinguishes it from the sibling utm-to-latlon, so an agent can route 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?

Contains explicit "When:" (computing coordinates, distances, bearings, areas from given points) and "Not for:" clauses that name the alternative tool utm-to-latlon. This is the when/when-not/alternative pattern at full strength.

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