Charles Proxy has been pretty good to me - it's straightforward with little setup. It could use more features but it does exactly what it advertises. I use it

Charles Proxy has been pretty good to me - it's straightforward with little setup. It could use more features but it does exactly what it advertises. I use it for security testing our website, making sure form data is properly handled, etc. It's also good for reverse engineering apis and can replace files with your own too.