lookup_cep

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

No annotations are provided, so the description carries the transparency burden. It discloses that the tool aggregates multiple providers (Correios, ViaCEP, and others), which is a useful behavioral detail. It also notes that geographic coordinates are returned 'when available,' honestly disclosing optionality. It doesn't mention error behavior for invalid CEPs, but the core behavioral profile is well covered.

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 tight and well-structured: one lead sentence stating the purpose, a concise list of returned fields, and a brief note about the underlying API. Every sentence earns its place with no filler or redundancy.

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?

The tool is simple (single required param), has an output schema to describe return values, and the description covers purpose, the data source, and the conditional nature of coordinates. For a straightforward lookup tool, this is complete. It could theoretically mention error/not-found behavior but that's a minor gap given the overall simplicity.

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?

Schema coverage is 100% — the single 'cep' parameter is fully described with format ('8-digit', with or without hyphen, e.g., 01310-100). The description doesn't add much beyond the schema because there's only one parameter and it's fully specified there. Baseline 3 is appropriate when schema handles parameter documentation.

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 uses a specific verb+resource ('Look up the full address for a Brazilian postal code (CEP)') and clearly states what it returns (street, neighborhood, city, state, geographic coordinates). It distinguishes itself from sibling tools like lookup_cnpj, lookup_ddd, and lookup_broker by being specifically about postal code lookup.

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 conveys usage context by naming the data source (BrasilAPI's CEP v2 endpoint) and listing returned fields. It doesn't explicitly say when NOT to use it or name an alternative tool, but there is no sibling tool that appears to compete with lookup_cep since all other lookup_* tools target different data types (companies, DDD, ISBN, brokers).

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