Serving scaled images is important! Here are some images that needed scaling on a client website.
And here is the before GTMetrix score:
Now, the images are then optimized so that instead of scaling them, they are the exact size displayed. We run GTMetrix again, and we find:
Now for the score improvement!
Note that image scaling is one of the metrics found on the GTMetrix score card. There are many more!
For example, under Page Speed:
And of course, there are others under the other tabs. Optimize them all, and you will have a beautifully optimized website.
We don't only use GTMetrix, we also use Pingdom. And of course, there is PageSpeed Insights. But PageSpeed Insights may not be your best friend, for this reason.
Other tools? Test my site, and Lighthouse are great!
Why so many tools? Everyone has a different idea about what "great" means. Our goal is to be "as great as possible" using all of these tools.
How much time does it take to optimize a website, anyway? That depends. You might be able to do it in a day, or two days. In some cases, it will take longer.