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

No annotations are provided, so the description carries the full burden. It usefully discloses the auth requirement (API key via x-api-key) and the shape of the return data, which is valuable given there is no output schema. It says nothing about rate limits, cost, error behavior, or data freshness relative to the realtime sibling.

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 short sentences, front-loaded with the purpose, then the return values, then the auth requirement. No filler and nothing redundant.

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 low-complexity two-parameter tool with no output schema, the description covers purpose, return fields, and auth. The one material gap is the failure to differentiate from lookup_cpf_realtime, which an agent would need in order to choose correctly.

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%, so both parameters are already fully documented in the schema, including the accepted CPF formats and the optional-header fallback for api_key. The description adds no syntax or format detail 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 ('Consulta informações de um CPF brasileiro na CPFHub.io') and enumerates the returned fields (nome, data de nascimento, gênero). However, it does nothing to distinguish itself from the sibling 'lookup_cpf_realtime', which strongly implies a cached/database vs. real-time distinction that the description never addresses.

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?

No when-to-use guidance is given. The presence of 'lookup_cpf_realtime' as a sibling makes the missing selection criteria a real problem — an agent cannot tell which CPF lookup to pick. The description only notes that an API key is required, which is a prerequisite, not usage guidance.

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