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

Beyond the readOnly/idempotent/openWorld annotations, it discloses the actual mechanism: web search with per-CNPJ verification against the Receita. It also states the result cap (up to 5), the ordering (most likely first), and the normalization that filiais are collapsed into the matriz, which is behavior an agent could not infer from annotations alone.

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?

One compact paragraph, front-loaded with purpose, then mechanism, then return shape, then the interaction rule. Every clause carries distinct information and nothing is repeated from the title or schema.

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 description carries the return-value burden and does so well by naming razão social, nome fantasia, situação and cidade plus the ordering. The main omission is what happens when nothing is found or verification fails, which an agent would want to know before calling.

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 parameter with full schema coverage, so the baseline is 3. The description earns an extra point by clarifying that the name may be either razão social or nome fantasia, widening the semantic scope of the field beyond the concrete examples in the schema.

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?

The description states a concrete verb and resource ('Acha o CNPJ pelo nome da empresa') and immediately scopes the input to razão social or nome fantasia. No sibling tool performs anything comparable, so the agent can place it unambiguously.

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?

It gives an operational rule — 'Confirme com o usuário quando houver mais de uma' — which tells the agent what to do when the result set is ambiguous. It stops short of explicit when-not-to-use guidance (e.g., when the caller already has the CNPJ), which keeps it from a 5.

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