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

Beyond the annotations (read-only, idempotent, non-destructive), the description adds valuable context: it states that data is aggregated from official sources by EkoPump, that no authentication is required, and that prices are returned in euros per liter unless originally in another currency (already converted). These are non-obvious behavioral details.

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 concise and front-loaded with the core functionality. The Args section is somewhat redundant with the schema, but it is clearly formatted and every sentence contributes useful information (source, auth, return format).

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 return value scope (per country or all countries), the fuel types and Brent, and the currency/unit of prices. It is sufficient for an agent to invoke and interpret results correctly.

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 covers 100% of the parameter description, including the ISO format and the omission behavior. The description's Args section repeats the same information without adding new semantics beyond what the schema already provides, so the baseline score of 3 is appropriate.

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 uses a specific verb ('Devuelve') and clearly names the resource: national average prices for gasoline (G95), G98, and diesel per country, plus Brent oil price. This resource is distinct from sibling tools (alerts, city stations, country coverage), making it easy to distinguish.

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 implies its usage by describing it as a read-only data source, but it does not explicitly state when to use this tool over alternatives. It lacks any mention of alternative tools or exclusions, so the context is only implicit.

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