How to Validate Spanish NIF, NIE, CIF and IBAN in Any Programming Language (2026)

If you're building software for the Spanish market, sooner or later you'll need to validate fiscal documents. This guide covers everything: how the algorithms work, code examples in 4 languages, and the fastest way to add validation to any project.

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What are NIF, NIE and CIF?

• NIF — Tax ID for Spanish individuals (8 digits + 1 letter, e.g. 12345678Z)
• NIE — Tax ID for foreign residents in Spain (X/Y/Z + 7 digits + letter, e.g. X1234567L)
• CIF — Tax ID for Spanish companies (1 letter + 7 digits + 1 control char, e.g. A28015865). Also returns the company type: S.A., S.L., Cooperative, etc.
• IBAN — Bank account number, 24 characters for Spanish accounts (e.g. ES9121000418450200051332)

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Option 1: Implement it yourself

NIF validation (JavaScript)

const NIF_LETTERS = 'TRWAGMYFPDXBNJZSQVHLCKE';

function validateNIF(nif) {
  nif = nif.trim().toUpperCase();
  if (nif.length !== 9) return false;
  const number = parseInt(nif.slice(0, 8), 10);
  if (isNaN(number)) return false;
  return nif[8] === NIF_LETTERS[number % 23];
}

console.log(validateNIF('12345678Z')); // true
console.log(validateNIF('12345678A')); // false

NIF validation (Python)

NIF_LETTERS = "TRWAGMYFPDXBNJZSQVHLCKE"

def validate_nif(nif: str) -> bool:
    nif = nif.strip().upper()
    if len(nif) != 9:
        return False
    try:
        number = int(nif[:8])
    except ValueError:
        return False
    return nif[8] == NIF_LETTERS[number % 23]

print(validate_nif("12345678Z"))  # True

NIF validation (PHP)

function validateNIF(string $nif): bool {
    $letters = 'TRWAGMYFPDXBNJZSQVHLCKE';
    $nif = strtoupper(trim($nif));
    if (strlen($nif) !== 9) return false;
    $number = intval(substr($nif, 0, 8));
    return $nif[8] === $letters[$number % 23];
}

var_dump(validateNIF('12345678Z')); // bool(true)

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Option 2: Use an API (3 lines of code, any language)

If you don't want to implement and maintain the algorithms yourself — especially for CIF which is significantly more complex — you can use the Spain Document Validator API on RapidAPI. It's free for up to 500 requests/month.

JavaScript (fetch)

const response = await fetch(
  'https://spain-document-validator1.p.rapidapi.com/validate/nif?value=12345678Z',
  {
    headers: {
      'X-RapidAPI-Key': 'YOUR_API_KEY',
      'X-RapidAPI-Host': 'spain-document-validator1.p.rapidapi.com'
    }
  }
);
const data = await response.json();
console.log(data);
// { input: '12345678Z', valid: true, type: 'NIF' }

Python (requests)

import requests

response = requests.get(
    'https://spain-document-validator1.p.rapidapi.com/validate/cif',
    params={'value': 'A28015865'},
    headers={
        'X-RapidAPI-Key': 'YOUR_API_KEY',
        'X-RapidAPI-Host': 'spain-document-validator1.p.rapidapi.com'
    }
)
print(response.json())
# {'input': 'A28015865', 'valid': True, 'type': 'CIF', 'entity_type': 'Sociedad Anónima'}

PHP (cURL)

$curl = curl_init();
curl_setopt_array($curl, [
    CURLOPT_URL => 'https://spain-document-validator1.p.rapidapi.com/validate/iban?value=ES9121000418450200051332',
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER => [
        'X-RapidAPI-Key: YOUR_API_KEY',
        'X-RapidAPI-Host: spain-document-validator1.p.rapidapi.com'
    ],
]);
$response = json_decode(curl_exec($curl));
// $response->bank_name = "CaixaBank"

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API response examples

NIF:

{ "input": "12345678Z", "valid": true, "type": "NIF" }

CIF:

{
  "input": "A28015865",
  "valid": true,
  "type": "CIF",
  "entity_type": "Sociedad Anónima"
}

IBAN:

{
  "input": "ES9121000418450200051332",
  "valid": true,
  "type": "IBAN",
  "country": "ES",
  "formatted": "ES91 2100 0418 4502 0005 1332",
  "bank_code": "2100",
  "branch_code": "0418",
  "bank_name": "CaixaBank"
}

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When to use the API vs implementing it yourself

	DIY	API
Setup time	2-4 hours	5 minutes
Works in any language	Requires separate lib per lang	Yes
CIF entity type info	Extra work	Included
IBAN bank name lookup	Very complex	Included
Maintenance when rules change	Your problem	Automatic

The free tier (500 req/month) is enough for most small projects. Paid plans start at $9/month for 15,000 requests.

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The full API documentation and interactive playground is available at spanish-validation-api.vercel.app/docs.