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

Even though annotations already declare readOnlyHint, idempotentHint, and openWorldHint, the description adds substantial behavioral context: independent fetching per indicator, automatic retries with exponential backoff up to 3 attempts, Portuguese error messages, HTTP 404 semantics, no authentication or rate-limit disclosure, and JSON/structuredContent output behavior. This goes far beyond what the annotations convey.

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 dense but well-organized, front-loads the core purpose, and uses labeled sections such as 'Quando usar,' 'Quando NÃO usar,' 'Retorna,' 'Resiliente,' and 'Comportamento.' Every sentence adds operationally useful information without 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 zero-parameter read-only tool with a rich output schema and annotations, the description fully covers use cases, exclusions, return shape, error handling, retry behavior, authentication requirements, and response format. An agent has everything needed to select and invoke this tool correctly.

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?

There are zero parameters, and the schema already represents this with an empty object. The description reinforces 'Não recebe parâmetros,' and with no parameters there is little additional semantic value to add. Baseline 4 is appropriate for a zero-parameter tool.

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 uses a specific verb ('retorna') and precisely enumerates the indicators returned in one call: Selic meta, IPCA mensal, IPCA acumulado 12 meses, dólar comercial de venda, and IBC-Br. It also distinguishes itself from siblings by naming bcb_serie_ultimos and bcb_serie_valores as the tools for historical or period-selected data.

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 explicitly states 'Quando usar: para um panorama econômico rápido' and 'Quando NÃO usar' for other series, historical data, or period selection, pointing to specific sibling tools. This is exemplary when-to-use versus when-not-to-use guidance.

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