Development tools for desktop browsers are as easy to access as right-clicking and selecting ‘Inspect Element.’ For mobile browsers its a little less intuitive to look at the code directly. Of course there are always different tools for testing responsive layouts. Some of these render in the browser you are testing which helps with basic functionality but doesn’t show the complete picture. Sometimes when you test on the actual device, the behavior is slightly different from the behavior you see on the desktop browsers. I’ve run into these issues with fonts rendering differently and mouse/touch events not working properly.
Using Safari with Xcode’s iOS simulator and/or your device can help. This little trick has helped me a lot over time and I don’t think its as well known about. It really is only a matter of using tools (most likely ones you already have on your machine) to work together. This is more of a tool for Mac users working on iOS devices. Great thing about this you can easily test internal and public sites.