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EU VAT validation on Vercel Edge

Add EU VAT validation to your Next.js app using Vercel Edge Functions. The edge runtime runs your validation globally with sub-50ms cold starts and built-in Next.js caching via next: { revalidate }.

Implementation steps

1. 1

   Create an API route with export const runtime = 'edge'

   Create app/api/validate-vat/route.ts and export export const runtime = 'edge' alongside the GET handler. The edge runtime restricts you to Web API-compatible code (no Node.js built-ins), but fetch, URL, Request, and Response are all available. Destructure country and vat from the request URL using new URL(request.url).searchParams to parse the incoming query parameters safely.

2. 2

   Store TAXID_API_KEY in your Vercel environment variables

   Add TAXID_API_KEY to your Vercel project's environment variables via the Vercel dashboard (Settings > Environment Variables) for Production, Preview, and Development environments. Access it in the edge function with process.env.TAXID_API_KEY — Vercel injects environment variables into the edge runtime the same way as the Node.js runtime. Never use next.config.js env for secrets, as those values are bundled into the client-side JavaScript.

3. 3

   Call the TaxID API with next: { revalidate: 3600 } for edge caching

   Inside your GET handler, call: const res = await fetch(`https://api.taxid.pro/v1/validate/${country}/${vat}`, { headers: { Authorization: `Bearer ${process.env.TAXID_API_KEY}` }, next: { revalidate: 86400 } }). The next.revalidate: 86400 option instructs Next.js's data cache to store this response for 24 hours at the edge, matching TaxID's cache window for active numbers and eliminating redundant origin requests for frequently-queried VAT numbers.

4. 4

   Return NextResponse.json to your React frontend or webhook handler

   Parse the TaxID response with const data = await res.json() and return NextResponse.json(data, { headers: { 'Cache-Control': data.status === 'active' ? 'public, max-age=86400' : 'no-store' } }). Setting Cache-Control on the edge function response tells Vercel's CDN layer how long to serve the cached response to subsequent requests for the same country+vat combination, providing a second caching layer on top of Next.js's data cache.

Code example

// app/api/validate-vat/route.ts
// Runs at the Vercel edge — global, sub-50ms cold starts

import { NextRequest, NextResponse } from 'next/server';

export const runtime = 'edge';

export async function GET(request: NextRequest) {
  const { searchParams } = new URL(request.url);
  const country = searchParams.get('country');
  const vat     = searchParams.get('vat');

  if (!country || !vat) {
    return NextResponse.json(
      { error: 'country and vat params required' },
      { status: 400 }
    );
  }

  const res = await fetch(
    `http://localhost:3000/api/v1/validate/${country}/${vat}`,
    {
      headers: { 'Authorization': `Bearer ${process.env.TAXID_API_KEY}` },
      next: { revalidate: 3600 },  // cache validated results for 1 hour
    }
  );

  const result = await res.json();
  return NextResponse.json(result);
}

# Test locally:
# curl "http://localhost:3000/api/validate-vat?country=DE&vat=DE123456789"

# Or call the TaxID API directly:
curl "http://localhost:3000/api/v1/validate/DE/DE123456789" \
  -H "Authorization: Bearer $TAXID_API_KEY"

# {
#   "valid": true,
#   "status": "active",
#   "company_name": "Example GmbH",
#   "cached": false
# }

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.

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