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

No annotations are provided, so the description carries the full burden. It discloses the tool's scope positively (what structural validations are performed) and negatively (no SAT registration check), and notes it is included with package balance. This is appropriate for a read-only validation tool, though it does not describe the response shape.

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?

Two sentences, front-loaded with the core purpose and followed by limitation and billing context. No 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 one-parameter validation tool with no annotations and no output schema, the description covers the essential context: what is validated, what is not validated, and cost implication. It lacks a description of the return value, but this is a minor gap for a validator.

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 single parameter 'rfc' has no schema description (0% coverage), so the description must compensate. It does so by defining the parameter's role—the RFC whose structure is validated—and by listing the validation dimensions. It does not specify the expected string format, but that is secondary.

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 ('la estructura de un RFC'), enumerating exactly what is checked: formato, tipo de persona, fecha y digito verificador. It also sets a clear scope boundary by explicitly saying it does not confirm SAT registration, distinguishing it from verification-focused siblings.

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 when to use the tool (for RFC structural validation) and provides an explicit when-not: 'No confirma que este registrado ante el SAT.' However, it does not name an alternative tool for SAT registration checks, so the guidance is clear but incomplete on substitution.

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