etfs_ranking

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

Since no annotations are provided, the description carries the full burden, and it delivers extensively: it explains data sources, same-day pricing calculation, liquidity cutoff, fee annualization, and that no API key is required. It also clarifies the output is descriptive, not a recommendation.

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?

Every sentence contributes distinct information: ranking criteria, valuation definitions, data provenance, liquidity filter, the descriptive nature, and access requirements. The most important scope appears early, and there is no filler.

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 tool with no output schema and no annotations, the description is unusually complete. An agent knows what metrics are returned, how they are calculated, which funds qualify, which data sources back them, and that authentication is unnecessary.

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 100% schema coverage, so the baseline is 4 because there is essentially nothing to document. The description redundantly states 'Sem parâmetros' and 'Gratuito — não exige chave,' which adds no parameter meaning but is harmless.

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 unambiguously identifies the resource: 'ETFs listados na B3' and enumerates the specific ranking dimensions (mais negociados, maior patrimônio, maior deságio/ágio, retorno de 12 meses, menor taxa efetiva). This clearly differentiates it from siblings like fiis_ranking or etf without ambiguity.

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?

It provides clear context: this is a descriptive ranking tool for B3 ETFs, with a liquidity threshold and an explicit 'não é recomendação' caveat. It does not explicitly name alternative sibling tools or say when not to use it, but the use case is clear enough for an agent to select it.

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