There are certainly many programs and browser extensions that can help with your question. If you want, you can find them on the Internet and download them. Well, if you want to check purchased proxy servers directly in your browser, you can use this tool called proxy checker online https://gobrowser.com/proxy-checker/.

Not long ago I bought proxies that I want to test for functionality before using them. Can you tell me how this can be done? Maybe there are some tools that can be used to fully test a proxy for all its features and shortcomings?