Katzilla MCP

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

Annotations already indicate this is a read-only, non-destructive, idempotent, and open-world operation. The description adds valuable context beyond this: it specifies the data source ('ReceitaWS'), update frequency ('daily'), rate limits implied by 'Free Tier', and the return format ('Katzilla envelope') with details on quality metrics and citation. This enhances the agent's understanding of reliability and auditability, though it doesn't detail exact rate limits or error handling.

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 efficiently structured in two sentences: the first states the purpose and source, and the second explains the return format and its components. Every sentence adds critical information without redundancy, making it easy for an agent to parse and apply.

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 (one parameter, read-only operation) and the presence of annotations and an output schema, the description is complete. It covers purpose, source, update frequency, return format, and data quality—addressing all necessary context for an agent to use the tool effectively without needing to explain basic parameters or output structure.

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 has 100% description coverage, fully documenting the 'cnpj' parameter with format examples. The description does not add any parameter-specific semantics beyond what the schema provides, such as validation rules or usage tips. With high schema coverage, the baseline score of 3 is appropriate, as the description relies on the schema for parameter details.

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 specific action ('Look up Brazilian company information'), the resource ('by CNPJ number'), and the source ('using the ReceitaWS API'). It distinguishes itself from siblings by focusing on Brazilian company data, unlike other government tools that target different countries or data types (e.g., 'government__congress-bills' for US legislation).

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 for when to use this tool: for Brazilian company lookups via CNPJ. It implies an alternative by mentioning the 'Free Tier' and 'updates daily', suggesting limitations that might require other sources for more frequent or comprehensive data. However, it does not explicitly name alternative tools or specify when not to use it, such as for non-Brazilian entities.

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