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

Annotations already cover read-only/idempotent/closed-world, and the description adds genuinely new behavior: the return payload is the 16 characters plus a per-group explanation, and the result is non-authoritative because of omocodice variants that only the Agenzia delle Entrate can settle. The rule that the catastale code valid on the birth date is used is a real behavioral detail, not a restatement.

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 tight sentences, front-loaded with what is computed and from what, then the place-resolution rule, then the return shape and the authority caveat. No filler and nothing redundant with the schema.

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, and the description compensates by describing the return value (16 characters plus per-group reasoning) and the non-definitive nature of the result. For a five-parameter, deterministic derivation tool this covers everything an agent needs before calling.

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 earns an extra point by explaining that birth_place accepts a comune with or without province, a foreign state, or a codice catastale/Z-code, and that the historical code at the birth date is applied — semantics the schema only gestures at.

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?

Specific verb (compute) plus a precisely scoped resource (the Italian codice fiscale) and an explicit standard (D.M. 23/12/1976) and full input list. Against siblings decode_/verify_codice_fiscale the direction of derivation (person data → code) is unmistakable from the first clause.

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?

Usage context is clear: derive a code from personal data, with place formats enumerated and support for the catastale code in force at the birth date. It never explicitly routes the agent to decode_codice_fiscale or verify_codice_fiscale, but the closing note that only the Agenzia delle Entrate confirms a code implies where verification belongs.

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