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

With no annotations, the description carries the full burden; it does disclose the cost profile ('Free') and the exact shape of a successful response via the example. However, it says nothing about error behavior for invalid/malformed CEPs, rate limits, or whether any auth is needed, leaving real behavioral gaps.

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?

Front-loaded with the purpose in the first clause, followed by the returned fields and a compact example. The example response is somewhat long but earns its place since no output schema exists.

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 one-parameter lookup with no annotations or output schema, the description supplies the full return field list and a concrete example, which is enough to call it correctly. The remaining gap is error/edge-case behavior.

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 100% and the single 'cep' parameter is already documented as '8 digits, e.g. 01001-000', so the baseline is 3. The description restates the resource but adds no format or validation detail beyond the schema.

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?

States a specific verb and resource ('Brazilian postal code (CEP) to address') and enumerates exactly what is returned (street, district, city, UF, IBGE code, DDD). This clearly separates it from sibling lookups like cnpj_lookup and bank_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?

Usage is implied by the name and the input framing, and 'Free' signals there is no cost barrier, but the description never states when to use this versus alternatives or any prerequisite. No explicit context or exclusions are given.

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