Google PageSpeed is Googles tool for identifying performance issues with your website. It is available both as an online tool and as a browser plugin.
Google PageSpeed loads your site and looks a number of different things in order to determine a score from 1-100. Scores are given in three categories, Mobile, Mobile Usability and Desktop. If you care about web performance, you should at least be aware of its existence and take a look at, and try to heed, any suggestions it might give you. There are also rumbling about PageSpeed scores influencing your search ranking which in itself makes it relevant to care about.
Google PageSpeed will tell you about the most important aspects of web performance such as:
Google PageSpeed doesn't actually evaluate the time it takes to load your full page, which is a significant drawback. It is also somewhat picky with the details. If a 1KB image file could be compressed down to 200 bytes that is considered very bad, where it in actually probably will not matter much.
| Site | Desktop Score | Mobile Score |
| Dev.to | 46 | 94 |
| Android | 61 | 72 |
| Microsoft | 69 | 63 |
| The Verge | 74 | 55 |
| Apple | 79 | 64 |
| This Blog | 100 | 100 |
Most websites don't score really high numbers in this test, for one reason or another. The most common culprits are blocking CSS and script files, and too large images. It is surprising to see Google do so poorly with Android.com as well as after all this is their tool, so maybe they should use it.
The most interesting example here on why there are some significant weaknesses in Googles approach is Dev.to, which get a horrible score, but is actually the second fastest site to load in your browser (after this blog). So as with any synthetic benchmark take these scores with a grain of salt.