lookup_cep

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the agent knows this is a safe, non-mutating lookup. The description adds the specific return fields (street, neighborhood, city, state, coordinates), which is useful behavioral context beyond the annotations. However, it doesn't disclose potential error behavior (e.g., invalid CEP, not found) or rate limits, which would be valuable for a lookup tool.

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 compact and front-loaded. The first sentence states the purpose and return data, and the Args section provides parameter guidance. Every sentence earns its place; there is no fluff or repetition of schema 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, single-parameter lookup tool with annotations covering the safety profile, the description is nearly complete. It covers what the tool does, what it returns, and how to format the parameter. The only gap is error handling behavior (e.g., what happens with an invalid or nonexistent CEP), but this is a minor omission for a read-only lookup tool.

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 description coverage is 0%, so the description must compensate. It does: it explains the cep parameter accepts a CEP number with or without formatting, providing examples ('01310930' or '01310-930'). This adds meaning beyond the schema, which only says the parameter is a string. The description could mention validation rules (e.g., 8 digits) but the format guidance is solid.

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 tool's purpose: looking up a Brazilian postal code (CEP) and lists the specific data returned (street, neighborhood, city, state, coordinates). This is a specific verb+resource combination that distinguishes it from siblings like lookup_cnpj, which looks up a different Brazilian identifier.

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 when to use this tool: when you need to look up a Brazilian postal code. It doesn't explicitly state when not to use it or name alternatives, but the sibling tools (lookup_cnpj, list_banks, get_holidays) are clearly different in purpose, so the usage context is reasonably clear. The description could be stronger with an explicit exclusion, but the context is sufficient.

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