Combustibles: ANCAP contra el precio de paridad de importación

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

Annotations already establish that the tool is read-only, idempotent, non-destructive, and open-world. The description adds important non-obvious context: the comparison is tax-exclusive, monthly since 2022, constructed by this server rather than an official figure, and the agent should read `metodo`.

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 opening question front-loads the tool's purpose, and the `Sin producto`/`Con producto` structure makes the two call patterns easy to scan. Every sentence contributes scope, mode behavior, or the non-official-metric caveat.

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 an output schema present and annotations covering safety, the description supplies the remaining context an agent needs: what is compared, the data scope, parameter modes, and the derived-metric caveat. No essential invocation detail 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 description coverage is 0%, so the description carries the full burden and largely succeeds. It defines `producto` as a mode switch, lists the four fuel products, and specifies that `desde` and `hasta` are AAAA-MM bounds for the series when `producto` is supplied.

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 opens with the exact decision question and then states the specific comparison: ANCAP ex-plant fuel price versus URSEA's import parity price, tax-exclusive, in $/litre, monthly since 2022. This is a clear verb+resource definition and identifies a comparison operation rather than generic fuel-price retrieval.

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?

It gives explicit conditional behavior for the two modes: without `producto` the tool returns the latest month and 12-month average for four fuels; with `producto` it returns a series and the latest PPI breakdown. It does not name sibling tools or when-not conditions, so it provides clear context but not full alternative routing.

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