Some hacks use a "Javascript Bookmark" that, when clicked, injects a cheat menu into an active Eaglercraft tab.
Here is a deep dive into what these clients are, how they work, and the risks involved. What is an Eaglercraft Hacked Client?
Draws boxes around players or entities through walls. How are they installed?
While the idea of having "superpowers" in a browser game sounds fun, there are significant downsides: