How can I limit my Mac to only one website during exams?

Just a heads up, any software solution you use to restrict access can usually be undone. I've seen people try that, even having to reinstall their OS at one point because they kept disabling the restrictions. It's worth asking yourself why you're looking to block everything except one site.

Honestly, the main issue might just be self-discipline. Training yourself to focus is key, even though I completely understand where you’re coming from. It could help to set restrictions on your own browsing habits.

You might want to check out an app called Safe Exam Browser. It's specifically designed for situations like this and can help lock you into just the one site you need during exams.

Have you thought about switching to paper or a Kindle for studying? It cuts out a lot of distractions and might help you concentrate better.