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

Annotations only declare readOnlyHint=true, and the description is consistent with that while adding real value: the enumerated status values (presunto, desvirtuado, definitivo, sentencia favorable), the returned notice numbers and dates, and the $0.02 USDC per-call x402 cost. It does not cover what happens for an RFC absent from the list, but the cost and return-shape disclosure go well beyond the 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?

Three short sentences, front-loaded with the action and target, then return values, then pricing. Every sentence carries distinct information with 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?

With no output schema, the description correctly compensates by naming the status vocabulary and returned fields, and it discloses the paid x402 model. For a one-parameter lookup this is nearly complete; only the no-match case and any latency/rate characteristics are unaddressed.

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?

There is a single required parameter with 100% schema description coverage, so the baseline is 3. The description adds no RFC format or normalization guidance (e.g. expected 12/13-character shape), so it does not supplement the schema meaningfully.

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?

States a specific verb and resource: checks an RFC against the SAT 69-B list, and defines that list as taxpayers with presumed non-existent operations (EFOS). The resource is clearly distinct from siblings like rfc_validar or sat_cfdi_verificar, but no sibling is named, so differentiation is inferred rather than stated.

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?

Usage is implied by the subject matter: this is the tool for EFOS/69-B screening rather than RFC format validation or CFDIs. It never explicitly says when to prefer it over rfc_validar or sat_cfdi_verificar, and there are no exclusions or prerequisites stated beyond the RFC input.

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