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

Annotations already declare readOnlyHint, destructiveHint, idempotentHint, and openWorldHint, covering safety and idempotency. The description adds the data source (BCB SGS), license (ODbL), and series number, but no additional behavioral traits like rate limits or pagination. With annotations carrying most of the burden, a 3 is appropriate.

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 a single sentence with 12 words, front-loading the key information: the series name, series number, and source. Every word earns its place.

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?

Given the existence of an output schema and complete annotations, the description covers the core purpose and series identifier. It could mention the frequency of the series (daily vs. monthly) but the parameter description partially covers that. Minor gap prevents a 5.

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 coverage is 100% and the parameter 'last_n' is fully described in the schema. The description adds no extra semantics about the parameter. Baseline 3 is correct.

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 clearly identifies the tool as providing the COPOM-set SELIC target rate with the specific BCB series number 4389. It distinguishes from sibling tools like finance.bcb.selic by specifying this is the target rate set by COPOM, not the effective rate.

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?

No explicit usage guidelines are provided. The description does not mention when to use this tool versus alternatives like finance.bcb.selic or finance.bcb.cdi. The contextual clue 'policy decisions' is not sufficient.

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