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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, and the description adds meaningful context beyond them: free (€0), no login required, deterministic, the comune field is always null, and 14 provinces are certainly wrong. These data-quality and access caveats are critical for an agent deciding whether to trust the result. There is no contradiction with the 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?

Three sentences all earn their place: the core function, the critical limitations, and the cost/auth summary. It is front-loaded with the main purpose and uses a compact list of example provinces. There is no redundancy or 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 single-parameter read-only tool with no output schema, the description covers scope, limitations, and auth/cost. It even names response fields like 'comune' and 'province_non_rappresentate', but does not name the main province field or describe behavior for invalid CAPs. It is nearly complete but relies on the agent infering some response details.

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%, so the baseline is 3. The description adds value by clarifying that the tool uses the 2-digit PREFIX of the CAP to determine the province, which explains why the result can be wrong for some provinces. It also reinforces the 5-digit format already in the schema. It doesn't cover validation behavior for malformed CAPs, so not a 5.

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: 'Restituisce la provincia del PREFISSO di 2 cifre di un CAP italiano' (returns the province of the 2-digit prefix of an Italian CAP). It also clearly differentiates itself by explicitly saying it does NOT return the comune. No sibling tool covers CAP lookup, so there is no ambiguity about what this tool does.

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 gives clear context: use it to get a province from a CAP prefix, and warns when not to rely on it ('per 14 province ... la provincia resa è SBAGLIATA con certezza'). It stops short of naming an alternative tool, but siblings contain no CAP lookup, so the guidance is effective. Without explicit when-to-use vs alternative wording, it doesn't earn a 5.

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