Leadgen ONRC Romania

Check a VAT number against EU VIES

check_vat

Read-onlyIdempotent

Check a Romanian VAT number against the EU's VIES register in real time: is it a valid VAT number today, under which name and address, and does that name agree with the company registry. Use it before invoicing a new supplier or when a buyer asks whether the VAT number on file is still live.

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": {
      "cui": "<cui>"
    },
    "name": "check_vat"
  }
}

Input Schema

Name	Required	Description	Default
`cui`	Yes	Romanian tax identification number (CUI), e.g. '2816464'; 'RO' and leading zeros are accepted.

Output Schema

Name	Required	Description
`name`	No	The name the EU holds for this number.
`error`	No	Set only when there is no answer (empty_query, invalid_cui, data_unavailable, plan_required ...); such a call is not counted.
`valid`	No	True when VIES says the number is a live VAT number.
`cached`	No	True when answered from the short-lived cache.
`reason`	No	Why the check did not run.
`source`	No	EU VIES.
`address`	No	The address the EU holds.
`checked`	No	False when VIES could not be reached.
`message`	No	A sentence for the caller.
`warning`	No	Present only on a mismatch.
`checkedAt`	No	When VIES answered.
`vatNumber`	No	The number as queried, e.g. RO14399840.
`nameMismatch`	No	True when the two names clearly disagree.
`registryName`	No	The name in the ONRC registry.

Schema Changelog

Changes observed during successful MCP inspections.

AddedNov 2, 2026

TDQS

A4.4/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds value beyond them by disclosing that the check is a live call to an external register ("in real time") and that the result is a point-in-time answer ("valid ... today"), which signals results can change between calls. It does not mention VIES downtime or rate-limit behavior, keeping it below a 5.

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, no filler: the first defines the operation and its three outputs, the second gives the triggering scenarios. The core purpose is front-loaded and the usage guidance follows logically.

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?

With an output schema present, the description needn't describe return values, and annotations cover safety; what remains is scope and timing, both addressed. The only gap is failure-mode behavior — what an agent should conclude if VIES is unreachable or returns no record — which matters for an external live lookup.

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% and the single parameter is already well documented with an example and the 'RO'/leading-zero tolerance, so the baseline is 3. The description earns the extra point by fixing the country scope as Romanian, which disambiguates the title's broader 'a VAT number against EU VIES' phrasing and warns the agent not to send other member states' numbers.

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?

States a specific verb and resource (check a Romanian VAT number against the EU VIES register) and enumerates exactly what comes back: current validity, registered name and address, and whether the name matches the company registry. None of the siblings perform VAT validation, so the tool is unambiguously separable from the lookup_* family.

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?

Gives two concrete triggering situations — before invoicing a new supplier, or when a buyer questions whether a VAT number is still live. That is real when-to-use guidance rather than implied usage. It stops short of naming alternatives or stating when not to use it (e.g. for non-Romanian VAT numbers).

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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