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

Annotations already mark it read-only and non-destructive. The description adds valuable transparency: no authentication needed, payment model (prepaid credits), public data nature, and LGPD compliance responsibility. This goes beyond the annotations without contradicting them.

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?

The description is front-loaded with the core purpose, followed by necessary context about credentials, payment, and data privacy. It is slightly longer than strictly necessary due to LGPD phrasing, but each sentence adds meaningful context.

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?

Given a simple lookup tool with no output schema, the description lists the returned fields (razão social, situação cadastral, natureza jurídica), and covers access, cost, and legal aspects. However, it omits behavior of the 'completo' parameter and any potential response differences, leaving a small completeness gap.

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 0%, so the description must compensate. It clearly identifies CNPJ as the input identifier, but the optional 'completo' boolean parameter is not explained at all. Partially compensates but leaves one parameter undocumented.

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 clearly states the tool's function: retrieving basic registration data (razão social, situação cadastral, natureza jurídica) from a CNPJ. It uses a specific verb ('consultar' implied) and resource (CNPJ), and the listed sibling tools are unrelated platform utilities, so it is well differentiated.

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 provides practical usage context: no credentials required, prepaid credit per query, and data is publicly accessible. It doesn't explicitly name alternatives or state when not to use, but given the sibling tools are generic, the context is sufficient for an agent to decide when to invoke this tool.

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