Home / Use cases / Deno

EU VAT validation in Deno

Validate EU VAT numbers in Deno using the built-in fetch API and TypeScript. Deployable to Deno Deploy with zero configuration — no npm install, no package.json needed.

Implementation steps

1. 1

   Use Deno's built-in fetch — no imports needed for HTTP

   Deno's global fetch is available in all contexts without any import. Define an async function validateVAT(country: string, vat: string): Promise<VATResult> that calls fetch(`https://api.taxid.pro/v1/validate/${country}/${vat}`, { headers: { Authorization: `Bearer ${Deno.env.get('TAXID_API_KEY')}` } }). The function is immediately usable in any Deno script without installing dependencies or modifying a package manifest.

2. 2

   Load the API key from Deno.env or a .env file

   In local development, create a .env file with TAXID_API_KEY=your_key and load it using Deno's built-in --env flag (deno run --env --allow-net --allow-env validate.ts). In Deno Deploy, set the environment variable in the project dashboard. Access it with Deno.env.get('TAXID_API_KEY') and throw an error at startup if it is undefined rather than silently sending unauthenticated requests.

3. 3

   Define a TypeScript interface for the VATResult response

   Declare: interface VATResult { valid: boolean; status: 'active' | 'invalid' | 'service_unavailable'; company_name: string | null; company_address: string | null; cached: boolean; request_id: string; }. Cast the parsed JSON to this interface with const result = await response.json() as VATResult. While this is a type assertion rather than runtime validation, combining it with a runtime check on result.status being one of the three known values adds a safety net against unexpected API changes.

4. 4

   Run with --allow-net --allow-env or deploy to Deno Deploy

   Execute locally with deno run --allow-net=api.taxid.pro --allow-env=TAXID_API_KEY validate.ts — scoping --allow-net to the specific domain restricts the script from making outbound calls to any other host, which is a stronger security posture than blanket --allow-net. For Deno Deploy, push the file to GitHub and connect the repository in the Deno Deploy dashboard; the runtime permissions are automatically granted to the deployed isolate.

Code example

// deno run --allow-net --allow-env validate_vat.ts
// Deploy to Deno Deploy — no npm install, no config

interface VATResult {
  valid: boolean;
  status: string;
  company_name?: string;
  company_address?: string;
}

async function validateVAT(
  country: string,
  vatNumber: string
): Promise<VATResult> {
  const res = await fetch(
    `http://localhost:3000/api/v1/validate/${country}/${vatNumber}`,
    { headers: { Authorization: `Bearer ${Deno.env.get("TAXID_API_KEY")}` } }
  );
  return res.json() as Promise<VATResult>;
}

const result = await validateVAT("DE", "DE123456789");

if (result.valid) {
  console.log(`Valid EU business: ${result.company_name}`);
} else if (result.status === "service_unavailable") {
  console.warn("VIES temporarily unavailable — retry later");
} else {
  console.log("Invalid VAT number");
}

curl "http://localhost:3000/api/v1/validate/DE/DE123456789" \
  -H "Authorization: Bearer $TAXID_API_KEY"

# {
#   "valid": true,
#   "status": "active",
#   "company_name": "Example GmbH",
#   "company_address": "Musterstraße 1, 10115 Berlin",
#   "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.

Related use cases