Vat

Validate Vat

validate_vat

Read-onlyIdempotent

Validate the FORMAT of a VAT registration number for the EU (+ UK/CH/NO), keyless & offline. Accepts the number with its country prefix ("DE123456789") or a national number plus country. Returns whether it matches the official country pattern. NOTE: format only — it does NOT confirm the VAT number is registered/active (use the EU VIES service for that).

Example tool call

This call uses example arguments supplied in the tool’s input schema.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "vat": "DE123456789"
    },
    "name": "validate_vat"
  }
}

Input Schema

Name	Required	Description	Default
`vat`	Yes	A VAT number, e.g. "DE123456789" or "GB123456789".
`country`	No	Optional 2-letter country code (EL for Greece, GB for UK) if `vat` has no prefix.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedJul 29, 2026

addedInput schema / examples

Added value: +[
+  {
+    "vat": "DE123456789"
+  },
+  {
+    "country": "FR",
+    "vat": "123456789"
+  }
+]

First observedJul 1, 2026

TDQS

A4.9/5.0

Behavior5/5

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

Adds key behavioral details beyond annotations: 'keyless & offline', format-only validation, and that it does not confirm active registration. No contradictions with annotations.

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?

Two sentences, front-loaded with purpose, then usage details and limitations. No irrelevant information.

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

Completeness5/5

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

For a simple validation tool with no output schema, the description covers purpose, parameters, behavior, and limitations adequately. Return value (boolean match) is implied.

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

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, baseline 3. Description adds value by explaining the two input patterns (prefix vs. national number + country) with examples, providing clarity beyond schema descriptions.

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 clearly states the tool validates the FORMAT of a VAT registration number for EU+UK/CH/NO. It distinguishes from siblings by noting it does not confirm registration, directing to VIES service.

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

Usage Guidelines5/5

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

Explicitly states two acceptable input formats (with prefix or separate country code) and clearly notes what the tool does NOT do (not a registration check), guiding when to use alternatives.

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

All Vat tools Inspect

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