Yes, responsive page testing is that easy! You don't have to learn another tool.
Can you paste an URL to the white field?... Tadaaaa! Magic happens!
You can easily resize your viewport by dragging, and see the effect in real time.
Presets help you to adjust width exactly to Bootstrap 3 breakpoints.
Refresh the page inside the custom viewport! Thanks to frames (yes,
browsers still support them) your page runs in a separate document and works