Crypto, web, finance and app data tools

EU VAT Number Check

eu_vat_check

Validate an EU VAT number live against the official EU VIES service, returning valid/invalid and the registered company name and address where the member state shares them. Use for B2B invoicing, reverse charge checks and KYC. Unavailable member states return an error and are not charged.

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": {
      "vat_number": "<vat_number>"
    },
    "name": "eu_vat_check"
  }
}

Input Schema

Name	Required	Description	Default
`vat_number`	Yes

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

AddedOct 22, 2026

TDQS

A4.2/5.0

Behavior4/5

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

With no annotations provided, the description carries the behavioral burden and does so well: it says validation is live against the official EU VIES service, explains what is returned, and notes that unavailable member states return an error and are not charged. It does not cover authentication or rate-limit behavior, but the core operational behavior is disclosed.

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 three tight sentences: purpose and return values first, use cases second, and unavailable-state behavior last. It is front-loaded and contains no filler.

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 one-parameter validation tool with an output schema, the description covers the main purpose, usage contexts, return content, and error/charging behavior. The only notable gap is VAT number format guidance, which is not covered by the schema either.

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?

The schema has only one parameter and 0% description coverage. The description clarifies that the input is an EU VAT number, but it does not specify expected format, country prefix, or examples, so it only partially compensates for the schema's lack of parameter documentation.

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: validate an EU VAT number against the official EU VIES service. It clearly distinguishes the tool from sibling validation tools such as iban_validate and email_validate by naming the exact validation domain and data source.

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 gives concrete usage contexts: B2B invoicing, reverse charge checks, and KYC. It does not explicitly name when not to use it or point to alternatives, but the intended context is clear.

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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