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

With no annotations, the description carries the disclosure burden and does useful work: it names the source (Autoridade Tributária portal), claims verification across all 308 municipalities, and discloses that per-parish municipalities return an explanatory answer instead of zero. It does not spell out the rate's format or year, but the core behavioral edge case is covered.

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?

Three short sentences, with purpose and input format front-loaded, provenance/verification in the middle, and the special-case behavior last. Every sentence contributes unique information 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 one-parameter lookup with no output schema, the description covers what the tool returns, the required input, the data source, reliability, and an important edge case. A minor gap is that the rate value's representation (e.g., percentage vs decimal) is left unspecified, but this does not block correct invocation.

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 coverage is 100%, and the schema already states that the municipality may be a name or four-digit code with examples. The description repeats that input capability without adding new semantic detail, so a baseline 3 is 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?

The description identifies the resource precisely ('yearly property tax (IMI) rate in one Portuguese municipality') and the accepted input forms. It does not explicitly contrast itself with siblings like imi_annual_cost or imt_calculate, but the word 'rate' and the tax type make the primary purpose unambiguous.

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 context of when to use the tool is implied: when an agent needs the IMI rate for a single Portuguese municipality. There is no explicit when-not-to-use guidance or reference to alternatives, nor any mention that imi_annual_cost should be used for cost rather than rate.

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