Agent Services (x402): compliance, company, procurement

EU VAT Number Check (VIES) ($0.02)

check_vat

Read-onlyIdempotent

[Company & tax] Verify an EU supplier's or customer's VAT number before invoicing or paying. Use when applying the reverse charge or onboarding a B2B counterparty in the EU. Price: $0.02 per call (USDC on Base, x402). Returns the x402 payment requirements unless payment_signature is given. Sample: /samples/vat-check

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": "<vat>"
    },
    "name": "check_vat"
  }
}

Input Schema

Name	Required	Description	Default
`vat`	Yes	EU VAT number with country prefix, e.g. DK34223858, DE129273398
`payment_signature`	No	Optional x402 v2 PAYMENT-SIGNATURE value, relayed unchanged to the endpoint. Omit to receive the payment requirements.

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 17, 2026

TDQS

A4.1/5.0

Behavior4/5

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

Annotations already cover read-only/idempotent/open-world, but the description adds meaningful operational context: price ($0.02 USDC on Base), the x402 payment flow, and that a call returns payment requirements unless payment_signature is supplied. It does not describe rate limits or behavior on invalid/unknown VAT numbers, so not 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.

Conciseness4/5

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

Front-loaded with a category tag, purpose, and usage, followed by pricing and return behavior. Dense but every sentence carries information; the sample path and payment mechanics are useful rather than 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?

With no output schema, the description appropriately explains the two-phase return behavior (payment requirements vs. result) and the payment model. It is complete enough to invoke correctly, though it omits the response shape of a successful VAT verification.

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 the schema already documents both parameters, including the country-prefix format and the payment_signature semantics. The description's 'Returns the x402 payment requirements unless payment_signature is given' largely restates what the schema says, so it adds little beyond the 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?

States a specific verb and resource: 'Verify an EU supplier's or customer's VAT number'. It is clearly distinguishable from the sibling check_eori (customs identifier) and supplier_check, giving an agent an unambiguous target.

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 concrete trigger conditions: 'before invoicing or paying', 'when applying the reverse charge', 'onboarding a B2B counterparty in the EU'. It lacks explicit when-not or a named alternative sibling, so it stops short of a 5.

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

All Agent Services (x402): compliance, company, procurement tools Inspect

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