Look up CNPJ in Go

This guide shows how to look up a CNPJ with the CNPJAPI REST API in Go, using the standard library's net/http package. The response comes as JSON, with fields in PascalCase (RazaoSocial, SituacaoCadastral, ...).

Prerequisites

Go 1.18+.
An API key from CNPJAPI. Create your account at https://app.cnpjapi.com.br and generate the key (see Authentication).

Simple lookup

With typed structs for the fields you use:

package main

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

type Empresa struct {
	RazaoSocial       string `json:"RazaoSocial"`
	SituacaoCadastral struct {
		Descricao string `json:"Descricao"`
	} `json:"SituacaoCadastral"`
}

func main() {
	const cnpj = "00776574000156" // only the 14 digits, without punctuation
	const apiKey = "cnpj_sua_chave"

	req, _ := http.NewRequest(http.MethodGet, "https://api.cnpjapi.com.br/"+cnpj, nil)
	req.Header.Set("Authorization", "Bearer "+apiKey)

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

	if resp.StatusCode != http.StatusOK {
		log.Fatalf("consulta falhou: HTTP %d", resp.StatusCode)
	}

	var empresa Empresa
	if err := json.NewDecoder(resp.Body).Decode(&empresa); err != nil {
		log.Fatal(err)
	}

	fmt.Println(empresa.RazaoSocial)
	fmt.Println(empresa.SituacaoCadastral.Descricao)
}

Handling errors and rate limits

When you exceed the per-minute limit or the monthly quota, the API responds 429 with a Retry-After header (seconds). Treat it as recoverable. This snippet also uses the strconv and time packages, so add them to your import:

import (
	"net/http"
	"strconv"
	"time"
)

// ...

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

switch resp.StatusCode {
case http.StatusTooManyRequests:
	espera, err := strconv.Atoi(resp.Header.Get("Retry-After"))
	if err != nil {
		espera = 60 // no valid header, wait a minute
	}
	time.Sleep(time.Duration(espera) * time.Second)
	// retry...
case http.StatusNotFound:
	fmt.Println("CNPJ não encontrado na base pública")
case http.StatusOK:
	// decode the body...
}

State Registration (IE, premium)

On a plan that includes State Registration (IE), look up a company's IE from the official SEFAZ source. Pass uf for a single state (1 credit) or omit it for the nationwide sweep (3 credits):

type RespostaIE struct {
	Resultados []struct {
		UF       string `json:"uf"`
		IE       string `json:"ie"`
		Situacao string `json:"situacao"`
	} `json:"resultados"`
}

req, _ := http.NewRequest(http.MethodGet, "https://api.cnpjapi.com.br/consulta/ie/"+cnpj+"?uf=SP", nil)
req.Header.Set("Authorization", "Bearer "+apiKey)

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

var ie RespostaIE
if err := json.NewDecoder(resp.Body).Decode(&ie); err != nil {
	log.Fatal(err)
}
for _, r := range ie.Resultados {
	fmt.Println(r.UF, r.IE, r.Situacao)
}

Full contract (fields, coverage, credits) at Look up the State Registration.

Next steps

Create your free account at https://app.cnpjapi.com.br and make your first lookup in minutes.