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

Annotations already establish read-only, idempotent, non-destructive behavior, and the description reinforces 'Nothing is stored' while adding real substance: data sources (Generalitat/Notariado registrations, Catalonia contracts, Madrid tax declarations), source period, read date, licence, and the ±5% banding rule. It stops short of a 5 only because return shape details border on output documentation the tool lacks elsewhere.

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 and Spanish versions are full duplicates of the same content, roughly doubling length with no new information. The lead sentence is well front-loaded, but the verbatim bilingual repetition is waste an agent must wade through.

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 no output schema, the description carries the return burden and does so thoroughly: €/m² or rent, municipal figure with source/period/read date/licence, % and euro difference, and the below/in-line/above band. An agent has everything needed to call and interpret it.

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%, so parameters (m2, modo, zona, precio_eur, municipio, language) are already fully documented in the schema. The description restates the buy/rent and m²-required-for-buy logic without adding format or edge-case detail, so the 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?

Uses a specific verb (compares) with a precisely bounded resource: one listing's price/rent vs. the published municipal figure, per source. It is clearly distinguishable from siblings like comparar_municipios (town-to-town) or precio_parada because it anchors on a single asking price.

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 clear context for when the result is appropriate and, importantly, the limits of its meaning ('town average, not a valuation of the flat'; 'rent average mixes all sizes'), which steers correct use. It never explicitly names an alternative sibling or says when not to use it, so it stops short of a 5.

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