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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. Beyond that, the description adds genuinely valuable behavioral context: no API key required, $0.05 USDC per successful call, and payment rails (x402, Base or Solana) — details the agent could not otherwise infer.

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?

Two tight sentences, front-loaded with what the record contains and then the cost model. No filler, and the pricing caveat is clearly separated from the data description.

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 usefully enumerates the returned fields, and it covers the payment/auth precondition. The main gap is the absence of sibling routing guidance, but for a single-parameter lookup this is largely complete.

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 `cnpj` parameter is well documented in the schema (14-digit, punctuation optional). The description adds nothing about the parameter beyond what the schema already provides, 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?

The description makes clear it returns a Brazilian company's CNPJ registry record, enumerating the specific fields (legal/trade names, status, opening date, activities, address, capital, partners). It does not explicitly differentiate itself from the similar us_company_lookup / uk_company_lookup / br_cpf siblings, leaving that to the country/identifier context.

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?

There is no explicit when-to-use guidance, no mention of when to prefer us_company_lookup or uk_company_lookup, and no prerequisites stated. The Brazilian-company scope is implied only by the resource name and title, not spelled out as a selection rule.

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