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EU VAT Validation for SaaS Businesses

SaaS companies selling B2B across EU borders must validate customer VAT numbers to legally apply reverse charge. Integrate the TaxID API into your checkout and subscription flow to avoid VAT liability on unverified customers.

Implementation steps

1. 1

   Get a free TaxID API key

   Sign up at taxid.dev/signup. No credit card required. Store the key as an environment variable in your SaaS backend — never client-side.

2. 2

   Add a VAT number field to your SaaS checkout

   Add a labeled VAT number input to your checkout or onboarding flow. Mark it as optional for consumers and required for customers who request B2B zero-rate treatment. Collect both the country code and the VAT number string.

3. 3

   Validate server-side before creating the subscription

   Before completing checkout, call GET /api/v1/validate/:country/:vat from your server. If status is 'active', flag the customer as reverse-charge eligible and store the validated company details. If 'invalid', return a form error. If 'service_unavailable', charge standard VAT and follow up.

4. 4

   Apply reverse-charge in your billing system

   Update the customer's billing record to reflect reverse-charge treatment. In Stripe, set tax_exempt: 'reverse'. In Paddle, use the customer tax ID field. In your own invoicing stack, add an 'RC' annotation to the invoice and set the VAT rate to zero.

5. 5

   Re-validate monthly for subscription customers

   Run a background job at least once a month that re-calls the TaxID API for every reverse-charge customer. Flag any returning 'invalid' for your finance team to review before the next invoice cycle. Use the batch endpoint (POST /api/v1/validate) to validate up to 25 numbers in one request.

Code example

const res = await fetch(
  'http://localhost:3000/api/v1/validate/DE/DE123456789',
  { headers: { 'Authorization': 'Bearer YOUR_API_KEY' } }
);
const { valid, status, company_name, company_address } = await res.json();

if (valid) {
  console.log(`Valid EU business: ${company_name}`);
} else if (status === 'service_unavailable') {
  // VIES is temporarily down — retry or allow with manual check
  console.log('VIES unavailable — check back in a few minutes');
} else {
  console.log('Invalid VAT number — charge local tax rate');
}

import requests

res = requests.get(
    "http://localhost:3000/api/v1/validate/DE/DE123456789",
    headers={"Authorization": "Bearer YOUR_API_KEY"}
)
data = res.json()

if data["valid"]:
    print(f"Valid: {data['company_name']}")
elif data["status"] == "service_unavailable":
    print("VIES temporarily unavailable")
else:
    print("Invalid VAT number")

API response

The TaxID API returns a consistent JSON response for every validation request:

{
  "valid": true,
  "status": "active",
  "country_code": "DE",
  "vat_number": "123456789",
  "company_name": "Example GmbH",
  "company_address": "Musterstraße 1, 10115 Berlin",
  "request_date": "2026-05-10T00:00:00.000Z",
  "cached": false,
  "request_id": "req_01j..."
}

Error handling

The API uses a consistent Stripe-style error format. Always handle service_unavailable separately — VIES has occasional downtime and you should not reject valid customers during outages.

Evaluating EU VAT APIs? Compare TaxID vs Vatstack, Vatlayer, Avalara →

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