Page Speed
Google Page Speed is one of the most used tools to measure the speed. Simple and Clean.
Increase the Speed!
Speed is one factor that contains many other aspects. It reveals both bad coding and other bad decisions. I mainly use these tools to measure the speed and find the cause of low speed. By following their recommendation piece by piece, you will also increase the speed.
web.dev
The other tool from Google gives more than measure the speed. You can create a report that show you what to do.
GTmetrix
Another test site with other ways to test. Along with web.dev maybe the most common. Note that your test results may be better running this test twice. Caching?
nibbler
nibbler measure many things. Amongst other the presence in Twitter and Facebook. Which may or may not be relevant.
Dareboost
Another very nice test page that goes deeper than speed only. You have 5 free test per months.
Grader
Another test page that goes deeper than speed only. Note you have to log in order to test.
Sitechecker
Another test page that goes deeper than speed only. Note you have to log in order to test.
Ionos
Another test page that goes deeper than speed only. Note you have to log in order to test.
SEOsitecheckup
Very nice test page that goes deeper than speed only. Note you cannot test more than one page per day for free.