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

With no annotations, the description carries the disclosure burden and does unusually well: it names two error conditions and codes, states those errors incur no credit charge, requires API-key auth, and notes deathYear is always present (number | null). It omits rate limits, latency/timeout behavior, and whether success consumes credits, so it is not complete.

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?

Four tightly packed sentences with the core purpose front-loaded, then return shape, error behavior, and requirements. No filler, though it is dense enough that the return-shape and error details momentarily crowd out the primary action.

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?

There is no output schema and no annotations, so the description must carry return semantics — and it does describe the payload (cadastral data, current situação, always-present deathYear) and error codes. The main remaining gap is no guidance on distinguishing this tool from its sibling lookup_cpf.

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 cpf, birth_date formats, and the optional x-api-key alternative are already documented in the schema — baseline 3. The description adds only the consequence of a birth_date mismatch, not new syntax or defaults.

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 um CPF brasileiro') plus scope and source ('em tempo real na Receita Federal pela CPFHub.io'). The 'tempo real' qualifier implicitly separates it from the sibling lookup_cpf, but the description never names that sibling, so an agent must infer which lookup to pick.

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?

Usage is only implied: 'em tempo real' suggests this is the live/authoritative variant versus the cached lookup_cpf, but there is no explicit when-to-use, when-not-to-use, or cost/latency tradeoff guidance for choosing between the two lookups. Prerequisites (CPF, birth_date, API key) are stated, which helps.

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