Validate up to 50 EU VAT numbers in one call. 1 credit per item that gets a real answer (unavailable_upstream items are free).
Args:
items: list of {"country_code": str, "vat_number": str}, max 50.
| Name | Required | Description | Default |
|---|---|---|---|
| items | Yes |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the transparency burden. It discloses non-obvious behaviors: the 50-item maximum, the per-item credit cost, and the fact that 'unavailable_upstream items are free.' This adds real behavioral detail beyond a generic 'validate' statement, though it does not cover error handling or response shape.
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 compact and well-structured: a clear first sentence states the core purpose, the second covers cost behavior, and the Args block precisely defines the input. Every sentence adds value with no redundancy.
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 simple single-parameter tool, the description is nearly complete: purpose, batch limit, item structure, and cost are all covered. The main gap is the absence of any description of the return format or possible response values, which would help because there is no output schema, but invocation itself is fully specified.
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?
The schema provides almost no parameter detail (items array with untyped objects, 0% schema coverage). The description fully compensates by specifying the exact item shape: 'items: list of {"country_code": str, "vat_number": str}, max 50.' This gives an agent everything needed to construct valid arguments.
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 opens with a specific verb and resource: 'Validate up to 50 EU VAT numbers in one call.' This clearly identifies the batch nature of the tool and distinguishes it from the sibling validate_vat by emphasizing the multi-item, single-call scope.
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 batch usage with 'up to 50... in one call' and contextualizes credit costs per item, but it never explicitly mentions the sibling validate_vat or gives criteria for choosing between batch and single validation. The usage context is present but not fully articulated.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Add one secure layer between your agents and this server.
The two tools are clearly distinct: one validates a single VAT number, the other validates up to 50 in a batch. There is no meaningful overlap or ambiguity about when to use each.
Both tool names follow the same validate_vat / validate_vat_batch pattern, sharing a clear verb and domain noun. The naming is predictable and consistent.
Two tools is minimal, but the server's scope is narrowly focused on EU VAT validation. A single and a batch variant cover the core need without unnecessary bloat.
The domain is VAT number validation, and both individual and batch validation are provided. There are no obvious missing operations for this narrow purpose.