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

There are no annotations, so the description carries the behavioral burden. It discloses that this is a live SAT validation, includes a 69-B check, and that the operation costs 'CFDI' credits, which is useful behavioral context beyond the basic action. It does not detail return values or failure modes, but the 'valida' framing makes the non-mutating nature reasonably clear.

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 two concise sentences with no filler: the purpose comes first, followed by the single input instruction and the cost warning. It repeats nothing from the schema or annotations and earns every word.

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 validation tool with no output schema, the description is largely complete: it names the validation checks, tells the agent what to send, and flags that the call is not free. The main omission is a clear statement of what the response will look like, but the validation nature makes that outcome fairly predictable.

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 zero schema description coverage for the only parameter, the description compensates by stating that the 'xml' field should receive the CFDI's XML. This gives real semantic meaning to the parameter, though it does not specify encoding, size limits, or whether the raw XML string is expected.

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 'Valida un CFDI' and specifies the exact validation checks: official XSD Anexo 20, live SAT status, and the issuer's 69-B cross-reference. This clearly identifies the resource and scope, distinguishing it from sibling tools like validar_rfc or verificar_empresa.

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 gives clear input instructions ('Envía el XML del CFDI en xml') and implies the use case, but it never explicitly states when to prefer this tool over alternatives or when not to use it. The agent must infer the choice from the resource type rather than being told.

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