If you are already working with code then I recommend Visual Studio Code since it has an excellent built-in diff tool. Visual Studio Code is a pretty good code editor in its own right so I think it's a good app to have installed along with your other development tools. I use it to work on miscellaneous projects outside of my main IDE.
To use its compare feature, you first need two files open. Then, from the explorer panel, right click the first file and click "Select for Compare". Then, from the explorer panel, right click the second file and click "Compare with Selected". A new tab will open which shows the two files side by side with differences highlighted.
Here is an example of the difference view:
Conveniently, you can also launch the difference view from the command line. Based on the documentation, it looks like you can launch it like this:
code -d /path/to/file1 /path/to/file2
code --diff /path/to/file1 /path/to/file2