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Validate alphanumeric CNPJ in JavaScript

The cpf library also exports cnpj, supporting numeric and alphanumeric bodies. CNPJ is Brazil's legal entity registration number. Its body contains 12 A-Z0-9 characters; the final two check digits remain numeric. The same validator handles both representations.

Validate numeric and alphanumeric CNPJ

npm install cpf

import { cnpj } from 'cpf'

cnpj.isValid('11.222.333/0001-81') // true
cnpj.isValid('12.ABC.345/01DE-35') // true
cnpj.isValid('12ABC34501DE35')     // true
cnpj.isValid('12ABC34501DE36')     // false
cnpj.isValid('12ABC34501DE3A')     // false: letter in a check digit

You can also import only the CNPJ namespace with import cnpj from 'cpf/cnpj'. In CommonJS, use const { cnpj } = require('cpf').

Normalize lowercase letters before validation

isValid and inspect expect uppercase letters. To accept lowercase input, normalize it and handle character or length errors.

function isValidCnpjInput(input: string): boolean {
  try {
    return cnpj.isValid(cnpj.normalize(input))
  } catch {
    return false
  }
}

isValidCnpjInput('12.abc.345/01de-35') // true

Keep the document number as text. Cleaning it with replace(/\D/g, '') removes letters that are part of the CNPJ; converting it to a number also loses leading zeros.

Inspect and classify input

cnpj.inspect('12ABC34501DE36')
// { valid: false, normalized: '12ABC34501DE36',
//   issue: 'INVALID_CHECK_DIGITS' }

cnpj.getKind('12ABC34501DE35')     // 'alphanumeric'
cnpj.getKind('11222333000181')     // 'numeric'
cnpj.getKind('12ABC')             // null

getKind classifies the structure; it does not verify the mathematical value of the check digits. Use isValid or inspect for that check.

Calculate check digits

cnpj.calculateCheckDigits('12ABC34501DE') // [3, 5]

The calculation uses modulo 11 and each character's ASCII value minus 48, as described in the Brazilian Federal Revenue Service's calculation manual (in Portuguese). Its Alphanumeric CNPJ program collects the official guidance. The library checks structure and check digits; it does not query existence, ownership or registration status.

See also CPF and CNPJ input masks and React integration.