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

With no annotations, the description carries the behavioral burden and does add the useful cost signal ($0.01 per call), which the agent cannot get from structured fields. It does not, however, state return format, whether the lookup is cached, or behavior on invalid/unknown CNPJ, so the disclosure is partial.

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 dense sentence covering resource, key, and returned fields, plus a short price note. Zero filler and the identity of the tool is front-loaded.

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?

For a one-parameter lookup with no output schema, listing the returned data fields substitutes meaningfully for a return-value description, and the price is disclosed. Missing only edge-case behavior (unknown CNPJ, error handling), which keeps it short of full completeness.

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%, so the single cnpj parameter (formatting optional, numeric or alphanumeric per IN RFB 2.229/2024) is fully documented in the schema. The description only restates 'by CNPJ' and adds nothing beyond the schema, 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?

States a specific verb (retrieval) and resource (Brazilian company registration data), keyed on CNPJ, and enumerates the returned fields (legal name, status, address, QSA, CNAE, capital). This distinguishes it implicitly from siblings like get_company_dossier and get_company_score, though it never names those alternatives 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?

No when-to-use guidance and no routing to alternatives such as get_company_dossier or get_company_score, both of which return related company data. Usage is only inferable from the field list; nothing tells the agent which sibling to pick or in what situation.

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