Working with various views inside the layout file to create a user interface isn’t always a straightforward process. Hierarchy Viewer, located in the Android SDK
tools directory, lets you see exactly how your widgets are laid out onscreen graphically. This format lets you clearly see a widget’s boundaries so that you can determine what’s going on inside the layout. Hierarchy Viewer, the ultimate tool to make a pixel-perfect user interface, also lets you magnify the display in the pixel-perfect view to ensure that images and UIs display flawlessly on all screen sizes and at all densities.