https://urlscan.io
urlscan.io is a service which analyses websites and the resources they request. Much like the Inspector of your browser, urlscan.io will let you take a look at the individual resources that are requested when a site is loaded.
The idea behind urlscan.io is to allow even inexperienced users to get a look at what a particular website is requesting in the background. For people new to modern web development, this will often have a certain wow-effect.