Does a CNPJ exist and is it active?

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

With no annotations, the description carries the full burden and does well: it discloses the payment model ($0.001 USDC via x402), its position as the cheapest paid check, and the exact payload fields (status, date, branch flag, state). It omits rate limits, auth beyond payment, and result formatting, so not a 5.

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 tight sentences, front-loaded with the core purpose and return fields, then the cost, then the rationale. Every sentence earns its place 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?

Given no output schema and no annotations, the description adequately covers what the agent gets back (existence + status + date + branch flag + state) plus the payment cost. Only the exact response format is unspecified, which is minor for a simple existence check.

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?

Single parameter with 100% schema coverage, so the schema already documents the CNPJ format ('14 digits, with or without punctuation'). The description adds no additional syntax or validation guidance beyond what the schema provides, so the baseline 3 applies.

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 (Checks) and resource (CNPJ against the official Receita Federal registry) and enumerates exactly what it returns: existence, status (Ativa/Suspensa/Baixada), date, HQ/branch flag and state. It is differentiated from the fuller siblings (cnpj_consultar_empresa_completo, cnpj_consultar_empresa) by its lightweight scope, though no sibling is named explicitly.

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 closing line ('Digit validation alone cannot tell a well-formed number from a real, active company') implies when to reach for it — real-world verification rather than format checking. But it never names the alternatives (cnpj_consultar_empresa, cnpj_consultar_empresa_completo) or states when to prefer the fuller tools, leaving routing to inference.

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