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 two genuinely useful traits: the merged data provenance and the paid model ($0.005 USDC per call via x402), which an agent must know before invoking. It says nothing about return shape, empty/match-miss behavior, or error cases.

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 tight sentences, front-loaded with the core purpose and identifiers, followed by provenance and cost. No filler or redundancy.

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 single-param tool with no output schema, the description should indicate what a result contains; it only hints at this via the provenance sentence. Cost and provenance are covered, but the return payload is left to inference.

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?

Only one parameter and schema description coverage is 100%, so the schema already documents 'query' and its accepted formats. The description merely restates those identifier types, adding no format details, precedence rules, or disambiguation 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 (lookup) and resource (Brazilian bank / payment institution) plus the four accepted identifier keys, which is far more specific than a tautology. However, it accepts CNPJ while a sibling cnpj_lookup also exists, and the description never clarifies the boundary between them, so sibling differentiation is only partial.

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 explicit when-to-use guidance and no mention of the sibling cnpj_lookup that overlaps on the CNPJ identifier. The provenance sentence ('merged from STR participant list and active Pix participant list') is data-source context, not usage guidance.

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