How to include Chrome DevTools in Electron?

Maybe I am misunderstanding, but you can just do ctrl + shift + I to pull up dev tools.

Or alternatively if you are wanting to do it programmatically, the way I do it is include the following lines in my main.js file that is passed to electron.

var app = require('app');
var BrowserWindows = require('browser-window');
    
app.on('ready', function(){
    mainWindow = new BrowserWindow({width:800, height:600});
    mainWindow.webContents.openDevTools();
}

I believe part of your problem may be that you aren’t waiting for the app to be ready before you try to do stuff with it.