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

The description discloses meaningful behavioral traits: it does not retain the full card number ('No se conserva el numero completo'), it is included with package balance ('Incluido con saldo de paquete'), and it does not confirm account/funds. These go beyond the sparse annotations, which only indicate no destructive action. There is no contradiction with annotations.

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 three sentences, front-loaded with the primary function and then adding behavioral notes. It is concise and free of fluff, but the behavioral notes are somewhat mixed in, and the structure could be improved by separating the core purpose from caveats. Still, it is efficient.

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 one-parameter validation tool with an output schema present, the description covers the purpose, input, and key limitations. It does not mention error conditions or expected output, but those may be in the output schema. The inclusion of package balance and non-retention adds useful context, making it reasonably complete.

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 coverage is 0%, so the description must compensate. It mentions the input 'pan' (card number) but does not elaborate on format, length, or examples. The description adds the fact that the PAN is sent, which gives some meaning, but it could be more explicit about the expected format. For a single standard parameter, this is acceptable but not outstanding.

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 states a specific verb ('Valida') and resource ('una tarjeta'), and specifies the method ('Luhn + BIN + marca'). It clearly distinguishes from sibling validation tools like validar_curp or validar_clabe, as each targets a different identifier type. The purpose is unambiguous.

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 usage for card validation and explicitly states what it does NOT do ('No confirma cuenta ni fondos'), which helps an agent avoid using it for account or fund checks. However, it does not explicitly name alternatives or provide a when-to-use vs. when-not-to-use condition beyond the negative limitation.

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