CNPJ Validation in Node.js

1. What is a CNPJ?

CNPJ (Cadastro Nacional da Pessoa Jurídica) is the Brazilian National Registry of Legal Entities. It is the mandatory identification number for every company, association, foundation, or any other legal entity operating in Brazil. The CNPJ is issued and managed by the Receita Federal (Brazilian Federal Revenue Service).

A CNPJ is required for:

• Opening bank accounts and obtaining credit
• Issuing invoices (notas fiscais)
• Signing contracts and participating in public procurement
• Tax filings and social security obligations
• Registering with state and municipal authorities

2. CNPJ anatomy

A CNPJ is a 14-digit number. When formatted, it uses the pattern XX.XXX.XXX/XXXX-XX. Internally, it consists of three parts:

3. The check digit algorithm

CNPJ uses two consecutive weighted MOD-11 sums. The first pass computes check digit 1 (position 13) from digits 1–12. The second pass computes check digit 2 (position 14) from digits 1–13 (including the freshly computed check digit 1).

First check digit (position 13)

1. Multiply each of the first 12 digits by the weight sequence: [5, 4, 3, 2, 9, 8, 7, 6, 5, 4, 3, 2]
2. Sum all products
3. Calculate remainder = sum mod 11
4. If the remainder is less than 2, the check digit is 0; otherwise the check digit is 11 − remainder

Second check digit (position 14)

1. Multiply each of the first 13 digits (including check digit 1) by the weight sequence: [6, 5, 4, 3, 2, 9, 8, 7, 6, 5, 4, 3, 2]
2. Sum all products
3. Calculate remainder = sum mod 11
4. Same rule: if the remainder is less than 2, the check digit is 0; otherwise 11 − remainder

Here is a step-by-step worked example for the CNPJ 11222333000181:

Here is a JavaScript implementation:

function validateCNPJ(cnpj) {
  // Strip formatting
  const digits = cnpj.replace(/[^\d]/g, '');
  if (digits.length !== 14) return false;

  // Reject known invalid patterns (all same digit)
  if (/^(\d)\1{13}$/.test(digits)) return false;

  const d = digits.split('').map(Number);

  // First check digit (position 13)
  const w1 = [5, 4, 3, 2, 9, 8, 7, 6, 5, 4, 3, 2];
  const sum1 = w1.reduce((acc, w, i) => acc + d[i] * w, 0);
  const rem1 = sum1 % 11;
  const check1 = rem1 < 2 ? 0 : 11 - rem1;
  if (check1 !== d[12]) return false;

  // Second check digit (position 14)
  const w2 = [6, 5, 4, 3, 2, 9, 8, 7, 6, 5, 4, 3, 2];
  const sum2 = w2.reduce((acc, w, i) => acc + d[i] * w, 0);
  const rem2 = sum2 % 11;
  const check2 = rem2 < 2 ? 0 : 11 - rem2;
  return check2 === d[13];
}

4. Why manual validation isn't enough

5. The right solution: one API call

The IsValid CNPJ API handles the full validation stack in a single GET request:

Get your free API key at isvalid.dev. The free tier includes 100 calls per day with no credit card required.

Full parameter reference and response schema: CNPJ Validation API docs →

6. Node.js code example

Using the @isvalid-dev/sdk package or the built-in fetch API (Node.js 18+):

// cnpj-validator.mjs
import { createClient } from '@isvalid-dev/sdk';

const iv = createClient({ apiKey: process.env.ISVALID_API_KEY });

// ── Basic validation ────────────────────────────────────────────────────────
const result = await iv.br.cnpj('11.222.333/0001-81');

if (!result.valid) {
  console.log('Invalid CNPJ');
} else {
  console.log('Formatted:', result.formatted);    // "11.222.333/0001-81"
  console.log('HQ?      :', result.isHeadquarters); // true
}

// ── With company lookup ─────────────────────────────────────────────────────
const detailed = await iv.br.cnpj('11222333000181', { lookup: true });

if (detailed.valid && detailed.found) {
  console.log('Company  :', detailed.razaoSocial);
  console.log('Trade    :', detailed.nomeFantasia);
  console.log('Status   :', detailed.situacao);
  console.log('CNAE     :', detailed.cnaeFiscal, detailed.cnaeDescricao);
  console.log('State    :', detailed.uf);
}

7. cURL examples

Basic CNPJ validation:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/br/cnpj?value=11.222.333/0001-81"

With company lookup via BrasilAPI:

curl -H "Authorization: Bearer YOUR_API_KEY" \
  "https://api.isvalid.dev/v0/br/cnpj?value=11222333000181&lookup=true"

8. Understanding the response

Valid CNPJ (basic)

{
  "valid": true,
  "formatted": "11.222.333/0001-81",
  "base": "11222333",
  "branch": "0001",
  "checkDigits": "81",
  "isHeadquarters": true
}

Valid CNPJ (with lookup)

{
  "valid": true,
  "formatted": "11.222.333/0001-81",
  "base": "11222333",
  "branch": "0001",
  "checkDigits": "81",
  "isHeadquarters": true,
  "found": true,
  "razaoSocial": "EMPRESA EXEMPLO LTDA",
  "nomeFantasia": "EXEMPLO",
  "situacao": "Ativa",
  "dataInicioAtividade": "2010-05-15",
  "cnaeFiscal": "6201501",
  "cnaeDescricao": "Desenvolvimento de programas de computador sob encomenda",
  "naturezaJuridica": "206-2 - Sociedade Empresaria Limitada",
  "porte": "ME",
  "capitalSocial": 50000,
  "uf": "SP",
  "municipio": "SAO PAULO",
  "cep": "01310100",
  "dataSource": "brasilapi"
}

Invalid CNPJ

{ "valid": false }

9. Edge cases to handle

const result = await validateCNPJ('11222333000262');

if (result.valid && !result.isHeadquarters) {
  console.log('This is a branch office (filial)');
  console.log('Branch number:', result.branch); // "0002"
  // Consider requesting the headquarters CNPJ instead
}

const result = await validateCNPJ('11222333000181', { lookup: true });

if (result.valid && result.found) {
  if (result.situacao !== 'Ativa') {
    console.log('Company is not active:', result.situacao);
    // "Baixada" = deregistered, "Inapta" = unfit, "Suspensa" = suspended
  } else {
    console.log('Company is active');
  }
}

// Both produce the same result:
const a = await validateCNPJ('11.222.333/0001-81');
const b = await validateCNPJ('11222333000181');

// Always store the raw form
const cnpjForDb = result.formatted.replace(/[^\d]/g, '');

// Use the formatted version for display
console.log('Display:', result.formatted); // "11.222.333/0001-81"

const result = await validateCNPJ('11222333000181', { lookup: true });

if (result.valid && result.found) {
  switch (result.porte) {
    case 'MEI':
      console.log('Sole proprietor (MEI)');
      break;
    case 'ME':
      console.log('Micro enterprise');
      break;
    case 'EPP':
      console.log('Small enterprise');
      break;
    default:
      console.log('Company size:', result.porte);
  }
}