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

Annotations already declare read-only, idempotent, non-open-world and non-destructive, so the safety profile is covered; the description adds real context on top: the upstream sources (Catastro statistics and Ministerio de Hacienda open data) and a hard coverage limitation that would otherwise cause silent bad answers for Basque and Navarran towns. It does not discuss response shape, but annotations plus the enumerated outputs carry most of that burden.

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?

A single front-loaded sentence that opens with the trigger and packs output fields, sourcing, downstream use and coverage caveats into one pass with no filler. It reads as a slightly run-on nested construction, which costs a little scannability, but every clause carries 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?

For a five-parameter, all-optional lookup with no output schema, the description covers what comes back, where it comes from, and where it stops being valid. The one notable gap is that with zero required parameters it never says an identifier (ine, or town plus province) is effectively mandatory to get a result.

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 the baseline is 3, but the description goes beyond the schema by tying tax_year to the concrete consequence of the 1.1% versus 2% rate choice, which explains why the parameter matters rather than just what it is. It still leaves the ine-vs-town/province selection entirely to 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?

States a specific resource (a Spanish town's cadastral values) and enumerates exactly what is returned: last general revaluation year, the resulting 1.1% vs 2% imputed-income rate, and the urban IBI rate on homes. It also positions itself against the sibling by naming estimate_modelo_210 as the consumer of the computed value, so an agent can tell the two apart 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?

"Use this when someone needs to know about..." gives an explicit trigger, and the description states a concrete handoff ("pass the revised value to estimate_modelo_210"), which clarifies the division of labour with that sibling. It adds a geographic exclusion (País Vasco and Navarra aren't covered), though it never frames a genuine alternative tool to prefer instead.

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