How does this actually help to make a site responsive?

[jcamp]

Very difficult to see how this would help make a website responsive?

[lexoyo]

it used to have a JS altorithm to force things to adapt but today it is just a help to visualize what your website looks like at several screen sizes, no matter the device you are on while checking (i.e you can see on mobile how it looks like on a big screen)

here is an example: http://www.responsize.org/?url=https://internet2000.net/