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

With no annotations provided, the description carries the full transparency burden. It discloses that the full PAN is not stored, that only Luhn/BIN/brand are checked, and that account/funds are not confirmed. It omits response behavior and side effects, but the key privacy and scope caveats are present.

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, front-loaded with the core action, and each sentence adds useful information. The 'saldo de paquete' sentence is somewhat peripheral to actually invoking the tool, and the phrasing is a bit staccato, so it is not a perfect 5.

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 one-parameter validator, the description covers the input and the tool's boundaries well. However, since there is no output schema, the lack of any hint about the result shape (boolean vs validation details) is a real gap, and the package-balance requirement is ambiguous.

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 schema has one required string parameter with 0% description coverage, so the description must compensate. It clarifies that the pan property is the card number to send and notes that the full number is not retained. It does not provide format, length, or accepted input examples, leaving some ambiguity.

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 the exact resource ('tarjeta') and the validation method (Luhn + BIN + marca). This is enough to clearly distinguish it from sibling validators like validar_clabe, validar_curp, validar_nss, and validar_rfc, even without naming them explicitly.

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 provides a clear boundary: the tool validates only Luhn/BIN/brand and explicitly does not confirm account or funds, so an agent can tell when not to use it. It does not name an alternative tool or give a direct when-to-use rule, so it stops short of a 5.

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