Yesterday, Google announced a new tool that uses two old tools designed to make it easier for small businesses to improve their site's mobile friendliness and page speed. So they combined the page speed and mobile friendly tool into one.
Interestingly enough, they also assigned a 0 out of a 100 score for mobile friendliness. Before it was pass or fail, not a score. This now gives you a score on how mobile friendly you are, which is interesting.
The tool is at testmysite.thinkwithgoogle.com and Google will then email you a report.
Here is the score for my corporate site which we recently redesigned.
Google will then email you a full report with details, if you want it. That report pretty much gives you the debugging you'd get from the more webmaster related tools.
Forum discussion at Local Search Forums.