I am currently testing my newly created webpage for responsiveness. Surprisingly, in Chrome Beta, there's no Macbook pro 13' device. When adding a new device, it's mandatory to fill "Device pixel ratio" and "User agent string". I seriously have no idea about these things. Any help will be good. :)

If it screen resolution emulation you want then you could simply dial in the required resolution.
The User agent string is generally used to identify what kind of device is making the request and could help if your backend differentiates between desktop and mobile clients that way.
Bhargav Voleti
Problem solver by nature. Traveller and musician by nurture.
Emil Moe
Senior Data Engineer
You can check your own agent: http://www.whoishostingthis.com/tools/user-agent/
And some other stuff.