cep

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

No annotations are present, so the description must disclose behavioral traits itself. It does state the return format ('Returns the address: state, city, neighborhood and street'), which is useful. However, it does not mention error handling, rate limits, or whether the operation is read-only (though that is implied for a lookup). The description adds some value beyond the schema but leaves room for more disclosure.

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 extremely concise, consisting of two short sentences that place the core purpose first and provide necessary format examples. Every sentence earns its place, with no filler or redundant information.

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 lookup tool with one parameter and no output schema, the description is largely complete. It states the input format and the output fields (state, city, neighborhood, street). It could mention potential error cases or the read-only nature, but given the simplicity of the tool, this is sufficient.

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 has no parameter description coverage, and the description compensates by clearly defining accepted formats: 'Accepts formats like "01001-000" or "01001000".' This goes beyond the bare schema field type and gives the agent actionable formatting guidance, which is highly valuable.

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' and the resource 'Brazilian postal code (CEP)', making the tool's function unambiguous. It does not explicitly distinguish itself from siblings like cnpj or ddd, but those are obviously different data types, so the absence of a named alternative is not a major drawback. It is specific and concise.

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 implies usage (a CEP lookup for Brazilian addresses) and provides format guidance, but it does not explicitly state when to use this tool versus alternatives or when not to use it. There is no mention of other tools or exclusions, so the guidance is implied rather than explicit.

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