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

Annotations already declare readOnly/idempotent/non-destructive, and the description goes beyond them by disclosing what the returned figure actually is (modeled advertised rent, not observed rent or a legal cap, with rent control explicitly out of scope) and what the response contains (hors charges, 95% interval, €/m², ANIL/DHUP segment). It doesn't cover freshness or data-source vintage, which keeps it short of 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?

Front-loaded with the core purpose, then usage examples, then the sibling alternative, then the caveat — a sound ordering with no filler. The first sentence is long and packs several output elements, which slightly taxes scanning, but no sentence is expendable.

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-value burden itself and does so (rent, interval, €/m², segment, optional yield), while also warning what the number is not. Nothing an agent needs to call this correctly on 4 simple parameters 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 coverage is 100%, so baseline is 3, but the description adds meaning the schema lacks: prix_achat is optional and only feeds the gross yield, and surface is optional with an example-surface fallback reflected in the answer. That connects the parameters to observable output behavior rather than restating the fields.

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 ("Loyer mensuel estimé d'UN logement") plus the exact inputs that define it (commune, typologie, surface), and explicitly contrasts with the sibling marche_commune. An agent can tell it apart from prix_m2_commune and marche_commune without opening the 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?

Gives concrete invocation examples ("combien louer un T2 de 40 m² à Nantes", "quel rendement pour ce T3 à 180 000 €") and names the alternative: "Pour le loyer médian et le rendement de marché de la commune entière, utiliser marche_commune". Both the when and the when-not are explicit.

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