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

The annotations already declare readOnlyHint=true and idempotentHint=true, and the description adds substantial behavioral context beyond them: it is deterministic, free, requires no login, always exposes base_iva and base_ritenuta separately, zeroes IVA for extraUE, and explicitly refuses to invent OSS rates for private EU consumers. No contradiction 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?

The description is dense but every sentence earns its place: first the core VAT calculation, then special regimes, then the critical two-basis rule, then cost/determinism/login guarantees. It is front-loaded with purpose and scoped to the tool's complexity.

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?

Given the tool's 8-parameter complexity, conditional intraUE logic, and absence of an output schema, the description plus detailed schema fully cover the essential business rules: OSS limitations, extraUE zeroing, two-base behavior, and ritenuta rates. The safety profile is already declared via annotations, and the description supplies the domain-specific caveats an agent needs.

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 description coverage is 100%, so the structured field descriptions carry the burden for parameters. The tool description adds useful high-level context about how contributo_integrativo and rivalsa_inps affect the two bases, but it does not meaningfully elaborate individual parameters beyond what the schema already says.

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: 'Calcola l'IVA italiana su un imponibile' with the exact rate set, optional ritenuta, and non-taxable regimes. It clearly differentiates the tool from siblings like calc_forfettario or calc_reverse_charge by focusing on ordinary Italian VAT on professional invoices.

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: it is for professional invoices where the contributo integrativo and rivalsa INPS create two distinct taxable bases, and it handles intra-UE/extra-UE non-taxable regimes. It does not explicitly name alternatives or state when not to use it, but the intended scope is evident.

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