Google has revamped and combined its tools for testing how mobile-friendly a website is and how quickly it loads. Simply enter the URL of the page here and wait for the results.
After a few seconds, you receive three levels of reporting. The first is a simple set of three scores: mobile-friendliness, mobile speed, and desktop speed.
Proceeding down the page (using the yellow arrow) you can click to see short lists of what needs fixing in each of the three areas (click on these thumbnails to see larger versions):
And at any point you can click the big blue button to have a detailed report sent to you: