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EU VAT validation in Go

Validate EU VAT numbers in Go using the standard net/http package. No external dependencies required — works with any Go 1.18+ project, from simple CLIs to high-throughput microservices.

Implementation steps

1. 1

   Import net/http and encoding/json from the standard library

   No go get is required — both packages ship with the Go standard library. Declare a VATResult struct with JSON tags matching the TaxID response fields: Valid (json:"valid"), Status (json:"status"), CompanyName (json:"company_name"), CompanyAddress (json:"company_address"), Cached (json:"cached"), and RequestID (json:"request_id"). This struct is your single source of truth for the API contract.

2. 2

   Build a GET request with the Authorization header

   Construct the URL as fmt.Sprintf("https://api.taxid.pro/v1/validate/%s/%s", country, vat) and create an http.Request with http.NewRequestWithContext(ctx, http.MethodGet, url, nil). Set the Authorization header with req.Header.Set("Authorization", "Bearer "+apiKey) using an API key loaded from os.Getenv("TAXID_API_KEY"). Always pass a context so the caller can enforce timeouts and cancel in-flight requests during graceful shutdown.

3. 3

   Decode the JSON response into map[string]any or a typed struct

   After executing the request with client.Do(req), check resp.StatusCode == http.StatusOK before decoding. Use json.NewDecoder(resp.Body).Decode(&result) where result is your VATResult pointer. Always call resp.Body.Close() in a defer statement to avoid connection leaks, which are especially impactful in high-concurrency services where leaked connections exhaust the connection pool.

4. 4

   Handle valid, invalid, and service_unavailable cases

   Switch on result.Status after decoding: case "active" proceeds with B2B reverse-charge logic; case "invalid" returns a validation error to the caller; case "service_unavailable" returns a sentinel error (e.g. ErrVIESUnavailable = errors.New("VIES temporarily unavailable")) that the caller can identify with errors.Is and handle by retrying or falling back to standard VAT rather than silently treating the number as valid.

Code example

package main

import (
  "encoding/json"
  "fmt"
  "net/http"
  "os"
)

func validateVAT(country, vatNumber string) (map[string]any, error) {
  url := fmt.Sprintf("http://localhost:3000/api/v1/validate/%s/%s", country, vatNumber)
  req, _ := http.NewRequest("GET", url, nil)
  req.Header.Set("Authorization", "Bearer "+os.Getenv("TAXID_API_KEY"))

  resp, err := http.DefaultClient.Do(req)
  if err != nil {
    return nil, err
  }
  defer resp.Body.Close()

  var result map[string]any
  json.NewDecoder(resp.Body).Decode(&result)
  return result, nil
}

func main() {
  result, _ := validateVAT("DE", "DE123456789")

  if result["valid"] == true {
    fmt.Println("Valid EU business:", result["company_name"])
  } else if result["status"] == "service_unavailable" {
    fmt.Println("VIES unavailable — retry later")
  } else {
    fmt.Println("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.

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