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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description earns credit beyond them by disclosing the external VIES/European Commission dependency, that denomination and address are returned only 'quando disponibili', and that the upstream call is skipped when the formal check fails.

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, front-loaded with the core action, followed by return content and the failure behavior. No filler and nothing repeated from the title.

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?

An output schema exists, so return values need not be explained, and the description still summarizes what comes back. It covers the external dependency and the short-circuit case; the only gap is routing guidance against the sibling validation tools and any note on upstream availability or rate limits.

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?

Only one parameter and schema coverage is 100%, with the schema itself specifying 11 digits and an example, so the baseline is 3. The description adds no format, normalization or error-handling detail about 'partita_iva' beyond what the schema already provides.

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 ('Verifica se una partita IVA italiana è attiva') plus the mechanism (VIES / Commissione Europea), so the agent knows exactly what it does. It does not name the closest sibling 'valida_partita_iva' explicitly, so the distinction is inferred from the formal-check sentence rather than stated.

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 is implied: the short-circuit sentence hints that a purely formal check is handled elsewhere, and the mention of 'attiva' implies a liveness check. But there is no explicit 'use this when / use valida_partita_iva instead' routing, which is exactly what sibling tools like valida_partita_iva and valida_codice_fiscale make necessary.

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