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

Annotations already indicate readOnlyHint=true, destructiveHint=false, idempotentHint=true, and openWorldHint=true. The description adds the specific return fields but does not disclose additional behavioral traits beyond what annotations provide. No contradiction with annotations.

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 sentence with 20 words, every part contributes to understanding. It includes necessary information (source/license) without unnecessary verbosity. Perfectly concise.

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 a rich output schema (not shown but implied), the description is complete. Annotations cover safety aspects, and the description adequately explains what the tool does without requiring additional context.

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% coverage, with the description of the 'cep' parameter repeating the tool's main purpose. The description adds minimal extra meaning beyond the schema, such as mention of optional dash. Baseline 3 is appropriate.

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 function: looking up a Brazilian address from an 8-digit CEP postal code, listing specific return fields (street, neighborhood, city, state, coordinates, timezone). It distinguishes itself from sibling tools (e.g., gov.brasilapi.cnpj) by focusing on postal codes.

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?

While the description does not explicitly state when to use this tool versus alternatives, its specific focus on CEP lookup and the context of sibling tools in the same domain make its usage clear. There is no explicit when-not-to-use guidance, but the purpose is straightforward enough.

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