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

Annotations already cover safety (readOnly, idempotent, non-destructive, openWorld). The description adds genuinely new behavioral context: it costs 1 request against the plan quota and is available on all plans, which is exactly what an agent weighing cost needs.

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, zero filler, front-loaded with the purpose before the cost and plan notes.

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?

With one parameter and no output schema, the description usefully states the return shape (name and CPF) plus the credit cost, which is what an agent needs before calling. It stops short of describing the not-found behavior or response format.

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?

There is a single required parameter with 100% schema description coverage, so the schema already carries the meaning. The description adds nothing about email format or normalization, so 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?

"Descobre a pessoa dona de um e-mail: nome e CPF" names a specific verb (reverse lookup) and resource (email) and even states the returned fields. It is clearly distinguishable from siblings like buscar_pessoa_por_nome or reverso_telefone, though it never names an alternative 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?

Usage is implied: you have an email and want the owning person's name and CPF. There is no explicit when-to-use versus the sibling name-search or phone-reverse tools, and no guidance on what to do when the lookup fails.

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