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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint, so 'Solo lectura' is consistent but partly redundant. The description adds genuine value by disclosing the authentication requirement and, usefully, the content of the result (balance plus euro equivalent) in the absence of an output schema. No error behavior or rate limits are mentioned.

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?

Three short sentences, front-loaded with what the tool returns, followed by the read-only note and the auth prerequisite. No wasted words.

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 single-optional-parameter read tool with no output schema, the description covers purpose, output content, and the login requirement, which is close to sufficient. It stops short of describing behavior when the customer is not logged in, leaving a minor gap.

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?

With one parameter at 100% schema description coverage, the schema fully documents the country enum and its effect on language, pricing and links. The description adds nothing about the country selector, so the baseline 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 names a specific resource — the customer's fichas balance (identified as Zacatrus's points program) plus its euro equivalent — and anchors it to 'Tu cuenta', which implicitly distinguishes it from the broader my_account sibling. An agent can tell exactly what is being retrieved.

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 states a prerequisite ('Necesita que el cliente haya iniciado sesión'), which is useful context, but gives no explicit when-to-use vs. alternatives (e.g., my_account) and no when-not guidance. Usage is implied by the resource itself rather than spelled out.

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