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

Goes well beyond the readOnlyHint/openWorldHint annotations: it discloses that CNPJ check digits are validated before any network call, the ~3 req/s upstream rate limit, the $0.003 USDC cost via x402 on Base/Solana/Arc, and crucially that failed calls are not charged. That is exactly the operational detail an agent needs before committing a paid call.

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?

Front-loaded with the purpose and source, then the field list, then the constraints. Dense but every clause earns its place; the parenthetical field enumeration is slightly list-like but useful for an agent matching fields to a user request.

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 an output schema present, return values need not be explained, and the description still covers cost, payment rail, rate limit, input validation, and billing behavior on failure. Nothing material is missing for a single-parameter paid lookup tool.

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 coverage is 100% and the single cnpj parameter already documents the 14-digit format with and without punctuation, so the description adds no parameter meaning beyond the schema. Baseline 3 applies when the schema fully carries the load.

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 ('Returns Brazilian company data'), names the upstream source (BrasilAPI, CNPJ lookup) and enumerates the returned fields, so an agent can distinguish it from company_fr, uk_company, and generic company_registry calls by jurisdiction alone.

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: the CNPJ parameter and the field list make clear it is for Brazilian entity lookups, but it never says when to prefer it over company_fr, company_registry, or sanctions/lei tools, nor any prerequisites beyond a valid CNPJ.

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