Documentação da API.

curl -s https://api.opencnpj.com.br/cnpj/06990590000123

const cnpj = '06990590000123';
const resposta = await fetch(`https://api.opencnpj.com.br/cnpj/${cnpj}`);

if (!resposta.ok) {
  throw new Error(`HTTP ${resposta.status}`);
}

const empresa = await resposta.json();
console.log(empresa.razao_social);
console.log(empresa.estabelecimento.situacao_cadastral);

import requests

cnpj = "06990590000123"
resposta = requests.get(f"https://api.opencnpj.com.br/cnpj/{cnpj}", timeout=10)
resposta.raise_for_status()

empresa = resposta.json()
print(empresa["razao_social"])
print(empresa["estabelecimento"]["situacao_cadastral"])

<?php
$cnpj = '06990590000123';

$ch = curl_init("https://api.opencnpj.com.br/cnpj/{$cnpj}");
curl_setopt_array($ch, [CURLOPT_RETURNTRANSFER => true, CURLOPT_TIMEOUT => 10]);
$body = curl_exec($ch);
$status = curl_getinfo($ch, CURLINFO_HTTP_CODE);
curl_close($ch);

if ($status !== 200) {
    throw new RuntimeException("HTTP {$status}");
}

$empresa = json_decode($body, true);
echo $empresa['razao_social'], PHP_EOL;
echo $empresa['estabelecimento']['situacao_cadastral'], PHP_EOL;

package main

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

type Empresa struct {
	RazaoSocial     string `json:"razao_social"`
	Estabelecimento struct {
		SituacaoCadastral string `json:"situacao_cadastral"`
	} `json:"estabelecimento"`
}

func main() {
	resp, err := http.Get("https://api.opencnpj.com.br/cnpj/06990590000123")
	if err != nil {
		panic(err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		panic(fmt.Sprintf("HTTP %d", resp.StatusCode))
	}

	var empresa Empresa
	if err := json.NewDecoder(resp.Body).Decode(&empresa); err != nil {
		panic(err)
	}
	fmt.Println(empresa.RazaoSocial)
	fmt.Println(empresa.Estabelecimento.SituacaoCadastral)
}

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;

public class ConsultaCnpj {
    public static void main(String[] args) throws Exception {
        String cnpj = "06990590000123";

        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create("https://api.opencnpj.com.br/cnpj/" + cnpj))
            .header("Accept", "application/json")
            .GET()
            .build();

        HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
        if (response.statusCode() != 200) {
            throw new RuntimeException("HTTP " + response.statusCode());
        }
        System.out.println(response.body());
    }
}

using System.Net.Http.Json;
using System.Text.Json;

var cnpj = "06990590000123";
using var http = new HttpClient();

var empresa = await http.GetFromJsonAsync<JsonElement>(
    $"https://api.opencnpj.com.br/cnpj/{cnpj}");

Console.WriteLine(empresa.GetProperty("razao_social").GetString());
Console.WriteLine(empresa.GetProperty("estabelecimento")
    .GetProperty("situacao_cadastral").GetString());

require "net/http"
require "json"

cnpj = "06990590000123"
resposta = Net::HTTP.get_response(URI("https://api.opencnpj.com.br/cnpj/#{cnpj}"))
raise "HTTP #{resposta.code}" unless resposta.is_a?(Net::HTTPSuccess)

empresa = JSON.parse(resposta.body)
puts empresa["razao_social"]
puts empresa.dig("estabelecimento", "situacao_cadastral")

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let cnpj = "06990590000123";
    let url = format!("https://api.opencnpj.com.br/cnpj/{cnpj}");

    let empresa: serde_json::Value = reqwest::blocking::get(url)?
        .error_for_status()?
        .json()?;

    println!("{}", empresa["razao_social"]);
    println!("{}", empresa["estabelecimento"]["situacao_cadastral"]);
    Ok(())
}

import 'dart:convert';
import 'package:http/http.dart' as http;

Future<void> main() async {
  const cnpj = '06990590000123';
  final resposta = await http.get(Uri.parse('https://api.opencnpj.com.br/cnpj/$cnpj'));

  if (resposta.statusCode != 200) {
    throw Exception('HTTP ${resposta.statusCode}');
  }

  final empresa = jsonDecode(utf8.decode(resposta.bodyBytes)) as Map<String, dynamic>;
  print(empresa['razao_social']);
  print(empresa['estabelecimento']['situacao_cadastral']);
}

import Foundation

struct Empresa: Decodable {
    let razaoSocial: String?
    let estabelecimento: Estabelecimento

    struct Estabelecimento: Decodable {
        let situacaoCadastral: String?
    }
}

let url = URL(string: "https://api.opencnpj.com.br/cnpj/06990590000123")!
let (data, response) = try await URLSession.shared.data(from: url)

guard (response as? HTTPURLResponse)?.statusCode == 200 else {
    throw URLError(.badServerResponse)
}

let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
let empresa = try decoder.decode(Empresa.self, from: data)

print(empresa.razaoSocial ?? "")
print(empresa.estabelecimento.situacaoCadastral ?? "")

USING OpenEdge.Net.HTTP.*.
USING Progress.Json.ObjectModel.*.

DEFINE VARIABLE oClient   AS IHttpClient   NO-UNDO.
DEFINE VARIABLE oRequest  AS IHttpRequest  NO-UNDO.
DEFINE VARIABLE oResponse AS IHttpResponse NO-UNDO.
DEFINE VARIABLE oEmpresa  AS JsonObject    NO-UNDO.
DEFINE VARIABLE cCnpj     AS CHARACTER     NO-UNDO INITIAL "06990590000123".

oClient   = ClientBuilder:Build():Client.
oRequest  = RequestBuilder:Get("https://api.opencnpj.com.br/cnpj/" + cCnpj):Request.
oResponse = oClient:Execute(oRequest).

IF oResponse:StatusCode = 200 THEN DO:
    oEmpresa = CAST(oResponse:Entity, JsonObject).
    MESSAGE oEmpresa:GetCharacter("razao_social") VIEW-AS ALERT-BOX.
END.
ELSE
    MESSAGE "Erro HTTP" oResponse:StatusCode VIEW-AS ALERT-BOX.

#include "totvs.ch"

User Function OpenCNPJ()
    Local cCnpj   := "06990590000123"
    Local oRest   := FWRest():New("https://api.opencnpj.com.br")
    Local aHeader := {"Accept: application/json"}
    Local oJson   := JsonObject():New()

    oRest:SetPath("/cnpj/" + cCnpj)

    If oRest:Get(aHeader)
        oJson:FromJson(oRest:GetResult())
        ConOut(oJson["razao_social"])
        ConOut(oJson["estabelecimento"]["situacao_cadastral"])
    Else
        ConOut("Erro: " + oRest:GetLastError())
    EndIf
Return