So, apologies if this isn’t specifically related to Cloudflare services, but this is the Performance category after all…
Hopefully someone will find this useful 
Following are some links that I wish I had known about back when I was working to optimize my various sites for speed. It’s always wise to understand what’s going on under the hood, and Cloudflare offers a lot of services to improve/mitigate some common causes of slow page loading.
I am not affiliated with any of the following.
GTmetrix provides very in-depth performance analysis such as: PageSpeed and YSlow scores & insights, decent waterfall, load timings (TTFB, DOM, etc.) and keeps a history of tests so you can compare over time. Free registration allows for deeper history and monitoring.
Pingdom speed test offers similar functionality to GTmetrix but has a better waterfall IMO. The insights are somewhat lacking.
Google PageSpeed Insights seems to be the gold-standard but offers few features compared to the above. Loves to bark about unoptimized images.
Varvy page speed is another variant that offers similar diagnostics. Helpful tutorials as well.
There’s also the open-source tool Sitespeed.io that can run via Docker container that has a lot of features to check out if you want to take things a few steps further.
Of course you can always pop open the inspector or devtools to view waterfalls and whatnot in your own browser, but I find these sites useful for testing from various locales and also the insight they provide about the various components that may be impacting your site’s performance.
What tools have you come across that you find useful for measuring site performance?
