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

Annotations already declare readOnlyHint=true, destructiveHint=false, idempotentHint=true, and openWorldHint=true, which convey safety and idempotency. The description adds the source (Banco Central do Brasil) and a licensing note (BrasilAPI MIT) but does not elaborate on behaviors beyond what annotations provide, such as cache behavior or potential errors. Given the strong annotations, the description's contribution is minimal.

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 concise, consisting of two short sentences. It front-loads the key information (rates and source). The inclusion of 'BrasilAPI MIT' is slightly extraneous but not detrimental. The structure is clear and efficient.

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 read-only tool with one optional parameter and an output schema, the description is adequately complete. It identifies the rates, source, and the refresh option. The output schema exists, so the return format does not need to be described. However, the description could mention that it aggregates multiple rates to enhance completeness.

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 for its single parameter (refresh). The schema's description for refresh already explains its purpose. The tool description does not add any new meaning or context beyond what the schema provides, so it meets the baseline for high schema coverage.

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 specifies that the tool returns current SELIC, CDI, and IPCA rates from Banco Central do Brasil. It clearly states the resource (rates) and the verb (current). However, it does not differentiate from sibling tools like finance.bcb.selic, finance.bcb.cdi, and finance.bcb.ipca which provide individual rates, missing an opportunity to clarify the aggregated nature.

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 description provides no explicit guidance on when to use this tool versus alternatives. It lacks information about use cases (e.g., when needing all three rates in one call) or when not to use it (e.g., if only one rate is needed). The refresh parameter is mentioned but without context on typical usage frequency or caching behavior.

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