I use this free tool all the time: Responsive Design Testing

Yes I use it too. You will also want to use googles responsive test tool in webmaster tools, because google sometimes 'sees' pages differntly

Hey,

You can test your website responsiveness in these sites
1. Mobile Responsive Design
2. Above mention site Responsive Testing tool
or
You simply test it from your Computer by inspect element by clicking Responsive Design Mode 5th icon from the right side.

Thanks.