LINE message inspector for GAS

gistfile1.gs

var access_token = "<INPUT_YOUR_ACCESS_TOKEN>"; 
var exclude_messages = []; // Ref: https://developers.line.me/ja/docs/messaging-api/reference/#webhook-event-objects

function doPost(e) {
  var events = JSON.parse(e.postData.contents).events;
  events.forEach(function(event) {
    if (exclude_messages.indexOf(event.type) == -1) {
      reply(event);    
    }
  });
  
  return HtmlService.createHtmlOutput(JSON.stringify({}));
}

function reply(e) {
  var postData = {
    "replyToken": e.replyToken,
    "messages": [{
      "type": "text",
      "text": JSON.stringify(e, null, 2)
    }]
  };

  var options = {
    "method": "post",
    "headers": {
      "Content-Type": "application/json",
      "Authorization": "Bearer " + access_token
    },
    "payload": JSON.stringify(postData)
  };

  UrlFetchApp.fetch("https://api.line.me/v2/bot/message/reply", options);
}