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

Annotations already cover read-only, idempotent and non-open-world, and the description still adds real substance: no API key required, taxes (ICMS/PIS/COFINS) deliberately excluded, the `ticker` field is often null because distributors are subsidiaries, and the response carries source, license and citation. It doesn't discuss pagination or result cardinality limits, which is the remaining gap.

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?

Front-loaded with what the data is (source, units, tax basis) before the call modes, and every sentence carries operational or interpretive value. It is dense and slightly long, particularly the `ticker` explanation, but nothing is 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?

No output schema exists, so the description must describe returns — and it names the fields, the summary block (cheapest/median/priciest), the ticker nullability rule, and the included source/license/citation. An agent can call this correctly and interpret the response without further docs.

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 0%, so the description must carry all param meaning — and it does: `cnpj` is 14 digits and returns all validity periods of a single distributor, while `de`/`ate` are AAAA-MM-DD bounding the start of validity. It also defines the default no-argument behavior, which the schema cannot express.

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?

States a precise verb+resource: residential electricity tariff per distributor from ANEEL open data, in R$/MWh, subgrupo B1 conventional, since 2010. It also distinguishes its two operating modes (no arguments = latest tariff per distributor; `cnpj` = all validity periods for one distributor), so an agent knows exactly which behavior it will get.

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?

Explicit context for both call patterns: no-arg for a cross-distributor snapshot with summary stats, `cnpj` for a single distributor's history sliced by `de`/`ate`. It also excludes a likely mis-expectation ("Não é recomendação de investimento"). No sibling tool overlaps in domain, so there are no alternatives to name — which is the only thing keeping this from a 5.

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