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

Goes well beyond the annotations (readOnly/openWorld/idempotent/non-destructive) by disclosing data provenance (BrasilAPI with OpenCNPJ fallback), absence of completeness/freshness guarantees, no personal-data fields (sócios, e-mail, telefone), the MEI/empresário-individual omission of razão social/nome fantasia/endereço, per-source status in `fontes`, and that source errors do not yield empty lists. These are non-obvious behaviors an agent must know to interpret results correctly.

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?

Front-loads purpose then usage, and every subsequent sentence carries a real constraint (provenance, omissions, `fontes`, invalid-CNPJ rejection). It is slightly long and includes boilerplate disclaimers ('não é aconselhamento jurídico') that do not aid tool selection, keeping it from a 5.

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?

An output schema exists, so return-shape explanation is unnecessary, and the description usefully references the `fontes` field and error semantics. For a single-parameter lookup, it covers provenance, limitations and edge cases thoroughly.

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 single parameter's description already documents mask tolerance and pre-query check-digit validation. The description's 'com ou sem máscara' and 'CNPJ inválido é rejeitado antes de qualquer consulta' largely restate 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+resource ('Cadastro de empresa brasileira por CNPJ') and enumerates exactly what data it returns (situação cadastral, CNAE, porte, capital social, natureza jurídica, localização). It also names the sibling relatorio_completo as the alternative for a combined lookup, so the agent can distinguish it without opening schemas.

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?

Contains an explicit 'Quando usar' clause listing the qualifying data categories, plus an explicit exclusion/redirect: for cadastro combined with sanções/contratos/CVM, use relatorio_completo. This is exactly the when-to-use/when-not/alternative structure that earns top marks.

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