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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so safety is covered. The description adds genuinely new operational context: the call consumes 1 request and is available on all plans, which matters for an agent managing quota against siblings like consumo_do_plano and limite_do_plano.

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, and the payload (what you get back) is front-loaded before the cost and plan notes. Every sentence carries distinct 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?

With no output schema, the enumeration of returned fields (nome, CPF, operadora, WhatsApp) is exactly the right compensation, and the cost/plan notes complete the picture for a one-parameter lookup. Only the failure/not-found behavior is left unaddressed, a minor gap for a tool this simple.

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 already documents the DDD format, optional +55 and punctuation tolerance. The description adds nothing about the numero parameter, so the baseline of 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 ("Descobre o titular de um telefone") and enumerates exactly what comes back: nome, CPF, operadora, WhatsApp status. The phrase "de um telefone" implicitly distinguishes it from reverso_email and ficha_cpf, which key off other identifiers, but the differentiation is left to inference rather than stated.

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 by the input type — an agent can infer this is the phone-number reverse lookup. There is no explicit when-to-use guidance, no mention of when to prefer reverso_email or ficha_cpf, and no statement about what happens for a number not in the base.

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