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

Annotations already establish readOnly/idempotent/non-destructive, but the description adds genuinely useful behavior beyond them: price and rent belong to the town, never the station; source, period and read date are included; a missing figure is null with its reason. That null-with-reason contract is valuable since there is no output schema.

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 and well-ordered within each language, but the content is delivered twice (English and Spanish) for an evaluator that only needs one, roughly doubling length without adding information. The claims themselves are tight, but the duplication is wasteful.

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 present, the description carries the return-value burden and does so fully: per-stop fields, the town-vs-station caveat, provenance fields, null handling for missing figures, and the no-line fallback. 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 coverage is 100%, so the baseline is 3, but the description adds real semantic value by spelling out what happens when the optional linea is omitted (lists available lines). The language parameter is left to the schema/default, which is acceptable at full coverage.

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+resource: it returns the stops of a given Rodalies/FGC line, ordered from Barcelona outwards, each with price per m², rent and travel minutes. No sibling tool covers line/stop data, so an agent can distinguish it immediately from ficha_municipio or ranking_por_perfil.

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 clear condition for use ('For a Rodalies or FGC line with a read stop order') and explains the zero-argument fallback ('Without a line it lists the available lines'), which is important given linea is optional. It does not name or exclude specific sibling alternatives, 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.