Validate a CNPJ (free)

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

The description states the validation is 'local' and 'free,' which discloses that no external API calls or payments are involved. However, it does not describe the return value format or behavior on invalid input, leaving gaps in understanding the tool's complete behavior. Since no annotations are provided, the description bears the full burden but only partially meets it.

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 a single sentence of 12 words, front-loading the core action and modifiers ('Free local check-digit/format validation'). There is no redundancy or unnecessary detail, making it highly efficient for an AI agent to parse.

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 the tool's simplicity (1 parameter, no output schema), the description covers the purpose, scope, and cost. However, it omits the output type (e.g., boolean or error message), which is a notable gap for an agent deciding how to use the result. This reduces 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?

The input schema already describes the 'cnpj' parameter (14 digits, with/without punctuation) at 100% coverage. The description adds value by clarifying that the tool accepts 'numeric or alphanumeric' CNPJ, which is additional information beyond the schema. This helps the agent understand the full range of valid inputs.

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 that the tool performs 'check-digit/format validation' of a CNPJ, specifying it is 'free' and works on a 'single' CNPJ. This distinguishes it clearly from sibling tools like lookup_company or validate_documents, which have different scopes.

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?

The description explicitly mentions the tool is free and performs local validation, which guides the agent on when to use it (e.g., for quick, cost-free checks) and implies it should not be used for full company data retrieval. However, it does not explicitly name alternative tools or conditions to avoid.

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