Ideally you'd use Tandem along-side your text editor. It's not meant to replace writing code - I think in most cases it's easier to write code by hand than use a visual tools. Though, I think there are cases where it's easier to use visual tools against a live application preview for making small adjustments - that's where Tandem fits in.

Here's a better video demo to help demonstrate this:

https://www.dropbox.com/s/pc50x5m991j71ot/html-css-js-demo.m...