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

With no annotations provided, the description carries the full burden and does meaningful work: it discloses the per-call price and payment rail ($0.005 USDC via x402), a free first call per day, and the provenance of the merged data. It does not cover authentication setup or rate limits beyond the daily free call, keeping it short of a 5.

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?

Purpose is front-loaded in the first clause, followed by pricing and a concrete example. The example JSON is somewhat long, but since no output schema exists it earns its place by showing the return shape.

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?

There is no output schema, but the embedded example response shows the result structure (ispb, compe_code, short_name, cnpj, pix.participant), and pricing is disclosed, so an agent has enough to call and interpret it. Only minor gaps remain around error behavior and pagination for broad name queries.

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 is already documented, so the baseline is 3. The description restates the same identifier types without adding syntax, formatting, or disambiguation rules 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 (bank/payment institution lookup) plus the exact identifier types accepted (COMPE, ISPB, CNPJ, name). It also names the upstream sources (Banco Central STR and Pix participant lists), which distinguishes it from the similarly named cnpj_lookup sibling that resolves companies rather than banks.

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 accepted query formats imply when the tool applies, and the pricing sentence hints at the cost model, but there is no explicit when-to-use guidance or comparison against siblings like cnpj_lookup. An agent must infer that this is the right tool when the target is a bank rather than a company.

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