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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds substantive behavioral context beyond that: validation is performed offline and does not confirm account existence, plus it enumerates the actual checks performed and the derived fields. Only the return-shape detail is absent, but an output schema exists.

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, each carrying distinct information: what is validated, the Italian-specific extras, and the explicit limitation. The scope and limitation are front-loaded with 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 offline validator with an output schema, the description covers scope, algorithm, country-specific behavior, and the key negative guarantee. Nothing an agent needs to select or call the tool correctly is missing.

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?

With a single required parameter at 100% schema description coverage, the schema already documents the iban string and provides a spaced-format example. The description adds no formatting or syntax rules beyond what the schema states, so 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?

States a specific verb and resource ('Validazione offline di un IBAN') and pins down the exact algorithm and scope: mod 97, per-country length, plus CIN/ABI/CAB decomposition for Italian IBANs. This distinguishes it clearly from siblings like valida_codice_fiscale and valida_partita_iva.

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?

Makes the operating context explicit ('offline') and gives a clear boundary condition ('Non verifica l'esistenza del conto'), which routes the agent away from any account-existence tool. It does not name specific sibling alternatives or state when a different validator should be preferred, so it stops short of full routing guidance.

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