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

Annotations already provide strong behavioral cues (readOnly, idempotent, openWorld). The description adds value by specifying the exact data fields returned, which goes beyond the annotations. No contradictions or missing critical behavioral details.

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, clear sentence with no fluff. It efficiently conveys the tool's purpose, output details, and source (BrasilAPI MIT). Every word earns its place.

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, single-parameter tool with an output schema and comprehensive annotations, the description covers all essential aspects: what the tool does, what data it returns, and the data source. It is complete for the tool's complexity.

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 covers the single parameter 'cnpj' with a detailed description of format (14 digits, with/without punctuation). Since schema coverage is 100%, baseline is 3. The description only briefly mentions '14-digit CNPJ tax ID', adding no new meaning beyond the schema.

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 verb 'look up', the resource 'Brazilian company by 14-digit CNPJ tax ID', and lists the returned data (name, address, CNAE codes, etc.) and source (Receita Federal). This distinguishes it from sibling tools like gov.brasilapi.banks or gov.brasilapi.cep.

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 implicitly indicates when to use this tool: to retrieve Brazilian company data via CNPJ. While no explicit alternatives or exclusions are given, the tool's specificity makes the context clear. A higher score would require explicit 'when not to use' guidance.

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