When building a website designers and developers need to deal with Mobile Devices like Cell Phones and Tablets. Here are the best (free) ways to test mobile responsiveness from multiple mobile device types.

1. A Browsers built in ‘inspector’ or ‘developer tools’

• On Google Chrome its called ‘DevTools’ => hit the F12 key!
  

2. Responsive Design Checker

• An online resource for testing responsiveness based on Desktop and Mobile devices sizes.

3. Mobile Moxy

• Has a wide selection of mobile device user agents.

4. GeoPeeker

• Good for generically testing loading assets from remote resources – not mobile/responsive specific.