EU VAT Number Validator (VIES): Bulk Check, Proof & Alerts

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds genuinely new behavior: per-result pricing ($0.003 start, $0.002 per number checked) and the legal-proof semantics of the requesterVatNumber flag — information an agent cannot get from the annotations. It stops short of describing throughput or rate limits for bulk runs.

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?

Two tight sentences, front-loaded with what the tool does before the optional-flag and cost details. The pricing sentence is arguably extra but is decision-relevant for a paid tool, so little is wasted.

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?

With only two optional params, no nested objects and no output schema, the description covers the return fields, the legal-proof behavior and the cost model. A bulk-call tool could say more about batch size limits or per-item failure handling, but nothing essential to a correct invocation 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?

Schema description coverage is 100%, so both parameters are already fully documented in the schema, including the country-prefix formats. The description reinforces the consultation-number semantics of requesterVatNumber but adds no format or syntax detail beyond what the schema already provides — baseline 3.

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 (checks) and resource (EU VAT numbers) against a named registry (VIES), and spells out the returned fields (valid or not, registered name and address). An agent can distinguish this from unrelated siblings like search_eu_public_tenders or get_run_results without opening any schema.

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 implies when the optional requesterVatNumber path matters ('each check returns an official consultation number'), which is conditional context, but it never states when to prefer this tool, when not to use it, or how it relates to any alternative. Usage is inferred rather than instructed.

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