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

With no annotations, the description carries the burden of behavioral disclosure. It usefully states that the operation has no cost and describes the returned data, and the name 'consultar_saldo' strongly implies a read-only query. However, it does not explicitly say that no data is modified or mention any access limitations or freshness of the latest movements.

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 front-loaded: the first sentence names the main result areas (balance, uses, expiration, movements), and the second sentence adds a key condition (no cost). Both sentences earn their place with no redundant filler.

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, zero-parameter consulta tool, the description is nearly complete: it states what data is returned and that there is no cost. Since there is no output schema, it would benefit from a bit more detail on the response shape or the time range of 'últimos movimientos', but the current level is adequate.

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 has zero parameters and 100% schema description coverage, so there is nothing for the description to clarify about arguments. The description instead focuses on the result contents, which is appropriate for a parameterless tool.

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 identifies the resource as 'saldo de paquete' and enumerates the returned content: individual uses per product, expiration dates, and latest movements. It is clear that this is a balance-query tool, though it does not explicitly distinguish itself from the sibling consultar_uso, which may overlap in scope.

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?

No guidance is given on when to prefer this tool over alternatives such as consultar_uso or consultar_precios. The 'No tiene costo' note is useful but does not explain the intended use case or provide exclusions.

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