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

Annotations already declare readOnly and idempotent; the description adds that no authentication is needed and explains a currency conversion nuance. This provides useful behavioral context beyond the annotations, though it omits details like rate limits or data refresh, which are acceptable given the low bar set by annotations.

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 description is compact and well-organized: a clear purpose statement followed by a short args list. It front-loads the key content and avoids any unnecessary wording.

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 simple read-only tool with one optional parameter and no output schema, the description explains the data source, price units (euros per liter), and currency conversion behavior. It does not detail the exact response format, but that is not critical for straightforward data retrieval.

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?

The input schema fully documents the 'country' parameter (ISO code, optional, omission returns all), and the description repeats this with an example. Since schema coverage is 100%, the description adds no new parameter semantics, so the baseline score of 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?

The description clearly states the tool returns national average fuel prices for gasoline (G95, G98) and diesel by country plus Brent oil price, using the verb 'Devuelve' and identifying the resource. This distinguishes it from sibling tools (alerts, city stations, coverage).

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?

The description provides context on usage: it aggregates official sources and allows optional country filtering. It does not explicitly discuss alternatives or when not to use it, but the focused scope on fuel prices gives sufficient guidance for correct selection.

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