Hi Claudia, You can use Chrome Dev Tools and also BrowserStack. I tend to use both. BrowserStack is expensive, monthly fee, which is annoying if you only need to use it for QA a few weeks before release. You'll need to keep cancelling and restarting the plan on BrowserStack. You may get really far with Chrome Dev Tools, Safari Mobile Responsive, Firefox Responsive, IE Responsive Tools. BrowserStack is nice for really one reason: Test on many devices and they are real devices.