I watched the last training video by Jay and people were asking what does he use to tell if the sites were responsive.
He used an add-on to Chrome if I'm not mistaken but there is another option in your wordpress dashboard.
You can also use a filter to search for themes that are mobile responsive.
Making your theme responsive is a MUST. Most people search from their tablets or mobile phones.
This is a google ranking factor.
PleaseLIKE this training if it helped you. Thanks for watching.