Really nice visualization; I'll use this if anyone needs an explanation/sandbox on my team!
You could auto-name them with silly generated names or something; like what github does when you create a new repo
I would like to know this as well...without the ability to create nested rows, I don't really see myself using this tool.
The nesting will actually "zoom" into the col you're putting it in and give you a new view, then you can zoom back out.
There IS a live HTML preview that you can actually see and drag your browser big and small.... but it's broke. Fixing it after work tonight.
rows will reset the col padding so nesting rows in cols will have the correct behavior.
Suggestions: There are some bugs. Sometimes I cannot drag to create an offset, sometimes I can. Also, sometimes I can only resize the col from the right. Would be nice to support containers (fluid and non-fluid) and we can better visualize how it impact the behavior in relation to the width of the device. Also, I think you can easily support Zurb Foundation grid too.
One suggestion: would it be possible to add old browsers as well? I am working on an app that doesn't render well on older versions of Firefox. I'll use Shoelace all the time for the front end part if I can use it to spot rendering problems with all kind of browsers.
Then using another size as xs let's you define the grid for bigger sreens while on small screens the content is just stacked vertically.
90% of my designs use col-sm-*, and then if stuff needs fiddling at md or lg I do it there. For xs I just usually let it default to stacked 100% cols.
Had made something similar before : http://jaykanakiya.com/bootstrap-grid-builder/
I wanted to attack the problem from a different angle than bootply and some of the others that recreate a WYSIWYG like Dreamweaver in the browser. This is JUST for seeing the grid and learning how it works, and seeing how the Less mixins work.
It's a narrow purpose, but I want to focus just on 1 thing and do it better than anyone in the world.
Grids on their own isn't as important as grids with content.
Still a great tool though, will come in handy.
That should be done tonight.
Be sure to check out the Less Mixin mode where you can name your rows and columns and use pure Less to make the grids.
Fun fact - it's all clojurescript.
PS: you mentioned Clojurescript, are you using Om?