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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description usefully adds the payment model — x402, Base or Solana, charged only on successful calls — which is real behavioral context an agent needs before invoking. It omits what happens on invalid or unknown CEPs (error vs empty result), which for a paid call is a meaningful gap.

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?

Two sentences, both load-bearing: the first states the lookup and its return fields, the second states cost and payment rails. Nothing is wasted and the purpose is front-loaded ahead of pricing.

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?

With no output schema, the description does supply the return shape (street, neighbourhood, city, state) plus the payment requirement, which is what an agent most needs to call it. Failure behavior for malformed or non-existent CEPs is the remaining omission, but the read-only, single-param design makes it minor.

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 parameter 'cep' is fully documented (8-digit, hyphen optional). The description adds no syntax or format detail beyond the schema, so the baseline 3 applies.

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 resource (Brazilian CEP) and enumerates the returned address fields (street, neighbourhood, city, state), so an agent knows exactly what it gets back. It does not explicitly distinguish itself from sibling Brazilian identifier tools (br_cnpj, br_cpf, br_ddd), but 'postal code (CEP)' is unambiguous enough to route correctly.

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?

There is no guidance on when to use this versus alternatives, no mention of input validity handling, and no stated exclusions. The only conditional content is about pricing (no API key → $0.05 USDC via x402), which is a cost notice rather than usage guidance.

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