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

Beyond the readOnly/idempotent/openWorld annotations, it discloses the real operational cost: 1 unit of the daily limit per partner returned, tracked in unidadesConsumidas, plus 1 hit on the per-minute limit, and which plans grant access. It also enumerates exactly what is returned, so the agent knows the payload shape without an output schema.

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 that front-load the purpose, then the output fields, then the cost and plan constraints. The parenthetical about partner-vs-company contact is the only long clause and it earns its place by preventing a common misread.

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 single-parameter lookup with no output schema, the description covers input, returned fields, quota consumption, and plan eligibility. Nothing an agent needs in order to decide to call it or to interpret the cost is missing.

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 100% and the cnpj parameter is fully documented, including punctuation tolerance and alphanumeric support, so the description adds nothing beyond 'Recebe um CNPJ'. Baseline 3 is appropriate since the schema carries the parameter semantics.

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 (receives a CNPJ, returns) and a precise resource (sócios pessoa física with nome, CPF, qualificação, telefones, e-mails), and explicitly distinguishes its output from the company-level phone in the Receita cadastro, which implicitly separates it from ficha_cnpj.

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 'o contato de cada sócio, não o telefone da empresa' clarification steers the agent toward this tool rather than the company record, and the plan list signals eligibility constraints. It never names a sibling tool or states an explicit exclusion, so it stops short of full when/when-not routing.

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