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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior. The description adds substantial context beyond that: quotes exist only on business days, non-USD parities come from Refinitiv and are not computed by the BCB, the disclaimer is passed through literally, and the response exposes consultation metadata. No contradiction with annotations.

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 long but well-structured and front-loaded with purpose, followed by usage guidance, return fields, defaults, and source caveats. The return-field enumeration is somewhat redundant with the output schema, but nearly every sentence carries useful decision-making or behavioral information.

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 output schema exists, the description does not need to explain return values, yet it still gives a useful field overview. It covers source attribution, business-day limitations, non-USD parity handling, disclaimers, and sibling-tool routing, making the tool callable correctly in nearly any context.

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%, so the baseline is 3. The description adds some rationale for defaults, like the 7-day window crossing weekends/holidays, but does not meaningfully extend the parameter semantics beyond what the schema already documents, such as date formats, limits, and default values.

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 states a specific verb and resource: 'Consulta a cotação PTAX de uma moeda contra o real' with date range support. It clearly distinguishes this tool from siblings by naming what it is not (long SGS series) and what it is (primary PTAX bulletin source with compra and venda in the same record).

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 gives 'Quando usar' and 'Quando NÃO usar' sections, naming bcb_serie_valores for long historical series and bcb_cambio_moedas for currency symbols. It also explains the default 7-day window as a way to cross weekends and holidays, giving concrete selection guidance.

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