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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered; the description adds genuinely new traits: no database access, no key required, no quota consumption. It also enumerates the response fields (cnpj, valido, formatado, alfanumerico, erro), which compensates for the missing 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 compact sentences, zero padding: purpose and local-only scope first, then return shape, then cost/credential implications. Every clause carries information an agent can act on.

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, read-only validation tool with no output schema, the description covers the essential surface: what is checked, that no backend is consulted, what fields come back, and the absence of quota/key requirements. Nothing needed to call it correctly 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 description coverage is 100%, and the description's note that the input may be numeric or alphanumeric, with or without punctuation, merely restates what the schema's cnpj description already states. No syntax, normalization or edge-case guidance is added beyond the schema, 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 and resource: it checks the format and check digits of a CNPJ locally, without querying the database. This directly separates it from the sibling consultar_cnpj, which presumably performs a registry lookup, so an agent can route between them from the description alone.

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 a base" plus "Sem chave e sem consumo de cota" gives a clear operational context (offline check, no credential or quota cost), which implies when to prefer this over a lookup tool. It stops short of naming consultar_cnpj as the alternative for registry data, so it is clear context without explicit alternative routing.

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