tollbooth

vat_validate

EU VAT number validation via official VIES. Validity, legal name, registered address for any EU business VAT ID.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "country_code": "<country_code>",
      "vat_number": "<vat_number>"
    },
    "name": "vat_validate"
  }
}

Input Schema

Name	Required	Description	Default
`vat_number`	Yes	VAT number without country prefix
`country_code`	Yes	2-letter EU member code e.g. IE, DE, FR

Schema Changelog

Changes observed during successful MCP inspections.

AddedOct 24, 2026

TDQS

A4/5.0

Behavior3/5

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

With no annotations provided, the description carries the behavioral burden. It usefully discloses that validation is performed via official VIES and that results include validity, legal name, and registered address, but it does not mention rate limits, error behavior, or what happens for invalid/non-EU numbers.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is two compact sentences with no wasted text. The purpose and returned fields are front-loaded and immediately useful.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple two-parameter read-only validation tool, the description covers the source, scope, and returned fields. Since an output schema is absent, it appropriately explains the return values, though it could mention error/edge-case behavior.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

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 well documented in the schema, including that vat_number excludes the country prefix and country_code is a 2-letter EU member code. The description adds no parameter-level detail beyond that baseline.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource: validating EU VAT numbers via official VIES. It also names the returned information (validity, legal name, registered address), making the tool's purpose unambiguous and distinguishable from unrelated sibling tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It clearly establishes the use case: validating any EU business VAT ID, with the scope limited to EU VAT numbers. It does not explicitly state exclusions or alternatives, but no close sibling tool appears to serve the same purpose.

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

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