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 behavioral burden. It usefully discloses the payment model and cost ($0.001 USDC via x402) and the authoritative data source (Receita Federal), which an agent needs before invoking. It omits other traits such as rate limits, auth requirements, and any safety/idempotency profile.

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 sentences, front-loaded with the core purpose, then cost, then justification. Each sentence contributes something distinct, though the 'cheapest paid check in the catalog' phrasing leans promotional rather than informational.

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?

Despite having no output schema or annotations, the description enumerates what is returned (existence, status, date, HQ/branch flag, state) and clarifies the paid-access model, giving an agent enough to call it correctly. Minor gaps around failure/error behavior remain.

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 description coverage is 100% and the single cnpj parameter is already documented as '14 digits, with or without punctuation'. The description adds no additional syntax or format guidance beyond the schema, so the baseline of 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 and resource ('Checks a CNPJ against the official Receita Federal registry') and enumerates the returned fields (existence, status Ativa/Suspensa/Baixada with date, headquarters/branch flag, state). It implicitly positions itself as the lightweight existence check versus the heavier siblings, though it never names cnpj_consultar_empresa or cnpj_consultar_empresa_completo directly.

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?

It justifies its own existence over naive digit validation ('Digit validation alone cannot tell a well-formed number from a real, active company'), implying usage for verification. However, it gives no explicit when/when-not guidance relative to the many overlapping cnpj_* siblings, leaving the agent to infer the choice.

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