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

Annotations already signal basic traits (readOnlyHint=false, openWorldHint=true, etc.), so the description's job is to add context. It adds the critical caveat that the tool does not confirm SAT registration, and mentions package balance inclusion, which hints at billing behavior. This goes beyond annotation data and helps set expectations.

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, all informative and front-loaded with the core purpose. The SAT registration caveat and package balance note are placed after the main function, maintaining a clean structure with no redundant phrasing.

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 tool with an output schema present, the description covers the essential purpose, validation scope, and a key limitation. The mention of package balance adds cost context. Missing details about RFC format expectations are minor given the single obvious parameter and validation-focused nature.

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%, but there is only one parameter (rfc), whose meaning is obvious from the tool name and description. The description implies that 'rfc' is the RFC string to validate and describes what validation checks, but does not specify input format constraints (length, case, pattern) beyond what validation implies. It adds some value but not enough to fully compensate for missing schema documentation.

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?

Description clearly identifies the resource (RFC), the action (validate structure), and specific aspects checked (formato, tipo de persona, fecha, dígito verificador). It also distinguishes itself from other validation tools by explicitly stating it does not confirm SAT registration, which is a unique qualifier among the sibling validar_* tools.

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 states what the tool does and explicitly excludes a common use case (confirming SAT registration), which helps agents avoid misuse. However, it does not name any alternative tools or provide explicit when-to-use versus sibling validar_* or verificar_* tools, leaving some inference required.

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