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

Annotations already declare readOnlyHint=true, openWorldHint=false and destructiveHint=false, so the safety profile is covered. The description adds two genuinely useful behavioral facts beyond them: it performs no external lookup and requires no API key/credential, which matters given the configurar_credencial sibling. It does not describe the response shape (boolean vs. structured error), a minor remaining gap.

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?

Two terse sentences, zero filler, with the core function stated first and the offline/no-key constraints following. Nothing could be removed without losing information.

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 one-parameter, read-only offline validator this is nearly sufficient: the agent knows what is checked, that nothing external is queried, and that no credential is needed. The only omission is how results are returned (valid/invalid flag, error detail), which there is no output schema to cover.

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 parameter is documented ('CNPJ com ou sem pontuação'), so the schema does the heavy lifting. The description adds only that formatting is checked, not anything about accepted input forms beyond what the schema states; 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 (confere) and resource (formato e dígitos verificadores de um CNPJ), making clear this is a structural validation rather than a registry lookup. The phrase 'sem consultar nada' implicitly separates it from the sibling consultar_cnpj, though it never names that sibling 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?

'Sem consultar nada. Sem chave.' implies the when-to-use condition (offline/format-only checks, no credentials required), which a careful agent can map against consultar_cnpj. However, no sibling is named and there is no explicit statement of when NOT to use it, e.g. when real registry data is needed.

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