validate_cpf

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It discloses the return shape ({ valid } and { reason } when invalid) and input format flexibility, but does not mention whether the tool is side-effect-free, whether it only validates check digits or also checks existence, or what specific reason values are possible. This is adequate but not thorough.

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 that is front-loaded with the action ('Valida um CPF brasileiro') and includes examples and return information without any unnecessary words. Every element earns its place, making it highly efficient.

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 tool with only one parameter, no output schema, and no nested objects, the description is fairly complete. It covers the input format, the validation purpose, and the output structure. The only minor gap is not enumerating possible reason values, but this is not essential for correctly invoking the 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?

The schema already describes the parameter at 100% coverage, but the description adds concrete examples ('529.982.247-25' or '52998224725') and clarifies the two acceptable input formats, which goes beyond the schema's minimal 'CPF formatado ou apenas dígitos' description and adds practical guidance.

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 'Valida um CPF brasileiro' (validates a Brazilian CPF), which is a specific verb+resource combination. It also distinguishes itself from sibling tools like generate_cpf and validate_cnpj by specifying validation of CPF specifically, and includes accepted formats to remove ambiguity.

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 provides clear context that this tool is for validating CPFs, making the intended use obvious. However, it does not explicitly mention alternatives or exclusions (e.g., 'for generating CPFs use generate_cpf'), so it lacks explicit when-to-use vs. when-not-to-use guidance, but the context is clear enough.

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