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

Annotations already carry readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered; the description still adds that no parameters or authentication are required and that the response includes an audit timestamp. It does not describe ordering or pagination, but for a fixed 27-item list that is minor.

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 purpose sentence followed by clearly labeled use / do-not-use clauses; every sentence maps to a decision the agent must make. The first sentence is long because it enumerates six returned fields, which is justified but slightly dense.

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?

With no input parameters and no output schema, the description compensates by enumerating the returned fields (state code, name, macro-region, station count, ICMS bracket, audit timestamp) and by stating prerequisites and auth needs. An agent has everything needed to call it correctly and interpret the result.

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?

The tool takes zero parameters and the description states that explicitly, so there is no parameter semantics to document. The schema is empty and fully consistent, making the baseline score appropriate.

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?

Names a specific verb and resource ('Returns the complete list of all 27 Brazilian Federative Units') and enumerates the payload fields. It explicitly distinguishes itself from the price-oriented siblings, so an agent can separate it from brazil_fuel_prices or brazil_compare_regions without opening any schema.

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?

Contains explicit 'When to use' (validate uf codes first, before four named tools) and 'When NOT to use' (not for actual commodity prices) sections with named alternatives. Both the selection condition and the exclusion are stated, leaving nothing to inference.

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