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

With no annotations provided, the description carries the full burden and does so excellently. It discloses the check algorithm, the rejection of all-same numbers, and the fact it is stateless with no recorded decision or dashboard trace—essential behavioral traits for an agent deciding to invoke 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?

Two sentences, front-loaded with the purpose, and every word adds value. No fluff or repetition of schema details.

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 simple validation tool with one parameter, the description covers purpose, algorithm, and side-effect profile. However, it lacks an explicit statement about the return value or output format, which would make it fully complete given there is no output schema.

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 provides only a 'cpf' string with zero description coverage. The description adds meaning by identifying it as a Brazilian CPF and elaborating on the validation logic, though it does not specify accepted formats (e.g., with/without punctuation).

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 explicitly states 'Validate a Brazilian CPF' and specifies the algorithm (mod-11 check digits) and a key edge-case (rejects all-same). This clearly distinguishes it from sibling validators like gstin_validate or iban_validate.

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 clearly implies use for CPF validation and adds the stateless/no-trace context, which informs when to choose it (e.g., when side effects must be avoided). However, it does not explicitly name alternative tools or exclusion scenarios, so it falls short of a 5.

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