cuducos.me
🇧🇷 CNPJ validation in Go
Adds support for alphanumeric CNPJ (July/2026)
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README.md
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README.md
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# Go CNPJ []()[](https://godoc.org/github.com/cuducos/go-cnpj)
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A Go module to validate CNPJ numbers (Brazilian companies unique identifier for the Federal Revenue).
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A Go module to validate CNPJ numbers (Brazilian companies' unique identifier for the Federal Revenue).
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> [!IMPORTANT]
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> Starting in July 2026 [the CNPJ number will be alphanumeric](https://www.gov.br/receitafederal/pt-br/acesso-a-informacao/acoes-e-programas/programas-e-atividades/cnpj-alfanumerico). This package **already supports the new format**. If you **do not** want to support the new format, tag this package to [`v0.1.1`](https://github.com/cuducos/go-cnpj/releases/tag/v0.1.1).
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```go
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package main
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// these return true
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cnpj.IsValid("11222333000181")
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cnpj.IsValid("11.222.333/0001-81")
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cnpj.IsValid("12.ABC.345/01DE-35")
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cnpj.IsValid("12ABC34501DE35")
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// these return false
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cnpj.IsValid("11.111.111/1111-11")
···
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cnpj.IsValid("AB.CDE.FGH/IJKL-MN")
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cnpj.IsValid("123")
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// this returns 11111111111111
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// these return 11111111111111 and 12ABC34501DE35
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cnpj.Unmask("11.111.111/1111-11")
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cnpj.Unmask("12.ABC.345/01DE-35")
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// this returns 11.111.111/1111-11
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// these return 11.111.111/1111-11 and 12.ABC.345/01DE-35
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cnpj.Mask("11111111111111")
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cnpj.Mask("12ABC34501DE35")
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}
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```
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cnpj.go
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cnpj.go
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import (
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"fmt"
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"regexp"
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"strconv"
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"strings"
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)
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func checksum(ds []int64, ref []int64) int64 {
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var s int64
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func checksum(ds []int32, ref []int32) int32 {
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var s int32
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for i, n := range ref {
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s += n * ds[i]
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}
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return 11 - r
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}
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//IsValid checks whether CNPJ number is valid or not
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// IsValid checks whether CNPJ number is valid or not
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func IsValid(n string) bool {
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u := Unmask(n)
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if len(u) != 14 {
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return false
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}
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ds := make([]int64, 14)
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for i, v := range strings.Split(u, "") {
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c, err := strconv.ParseInt(v, 10, 32)
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if err != nil {
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return false
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}
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ds[i] = c
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ds := make([]int32, 14)
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for i, v := range []rune(u) {
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ds[i] = int32(v) - 48 // ASCII value minus 48 so "0" becomes 0 and so on
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}
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r1 := []int64{5, 4, 3, 2, 9, 8, 7, 6, 5, 4, 3, 2}
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r2 := []int64{6, 5, 4, 3, 2, 9, 8, 7, 6, 5, 4, 3, 2}
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r1 := []int32{5, 4, 3, 2, 9, 8, 7, 6, 5, 4, 3, 2}
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r2 := []int32{6, 5, 4, 3, 2, 9, 8, 7, 6, 5, 4, 3, 2}
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return checksum(ds, r1) == ds[12] && checksum(ds, r2) == ds[13]
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}
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//Mask returns the CNPJ number formatted
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// Mask returns the CNPJ number formatted
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func Mask(n string) string {
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u := Unmask(n)
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if len(u) != 14 {
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return fmt.Sprintf("%s.%s.%s/%s-%s", u[:2], u[2:5], u[5:8], u[8:12], u[12:])
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}
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//Unmask removes any non-digit (numeric) from the CNPJ number
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// Unmask removes any non-digit (numeric) from the CNPJ number
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func Unmask(n string) string {
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return regexp.MustCompile(`\D`).ReplaceAllString(n, "")
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return regexp.MustCompile(`[^0-9A-Z]`).ReplaceAllString(n, "")
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}
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//Base returns the first 8 digits of the CNPJ number
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// Base returns the first 8 digits of the CNPJ number
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func Base(n string) string {
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if !IsValid(n) {
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return ""
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return Unmask(n)[0:8]
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}
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//Order returns the 9th, 10th, 11th and 12th digits of the CNPJ number.
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// Order returns the 9th, 10th, 11th and 12th digits of the CNPJ number.
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func Order(n string) string {
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if !IsValid(n) {
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return ""
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return Unmask(n)[8:12]
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}
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//CheckDigit returns the last 2 digits of the CNPJ number.
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// CheckDigit returns the last 2 digits of the CNPJ number.
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func CheckDigit(n string) string {
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if !IsValid(n) {
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return ""
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cnpj_test.go
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cnpj_test.go
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{"11111111111111", "11.111.111/1111-11"},
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{"123456", "123456"},
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{"11223344556677889900", "11223344556677889900"},
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{"12ABC34501DE35", "12.ABC.345/01DE-35"},
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} {
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if got := Mask(tc.cnpj); tc.expected != got {
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t.Errorf("Mask(\"%s\") = %v; expected %s", tc.cnpj, got, tc.expected)
···
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}
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func TestUnmask(t *testing.T) {
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if got := Unmask("11.111.111/1111-11"); "11111111111111" != got {
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t.Errorf("Unmask(\"11.111.111/1111-11\") = %v; want 11111111111111", got)
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for _, tc := range []struct {
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cnpj string
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expected string
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}{
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{"11.111.111/1111-11", "11111111111111"},
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{"12.ABC.345/01DE-35", "12ABC34501DE35"},
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} {
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if got := Unmask(tc.cnpj); tc.expected != got {
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t.Errorf("Unmask(\"%s\") = %v; want %s", tc.cnpj, got, tc.expected)
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}
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}
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}
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···
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{"11.222.333/0001-81", true},
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{"123", false},
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{"11.111.111/1111-11", false},
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{"12.ABC.345/01DE-35", true},
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{"12ABC34501DE35", true},
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{"12ABC34501DE42", false},
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{"12.345.678 9012-34", false},
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{"AB.CDE.FGH/IJKL-MN", false},
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} {
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if got := IsValid(tc.cnpj); tc.expected != got {
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t.Errorf("IsValid(%v) = %v; expected %v", tc.cnpj, got, tc.expected)
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t.Errorf("IsValid(\"%v\") = %v; expected %v", tc.cnpj, got, tc.expected)
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}
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}
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}