How do I check the functionality of a proxy?

I recently needed a proxy for work, I found some suitable ones and would like to check their functionality before using them. Can you tell me how to do this? Can I do it for free?

Yes, you can check the functionality of your current proxy completely free of charge with GoBrowser's online proxy checker. With their tool you can find out everything about your proxy, its type, country, city, speed and anonymity level. All you need to do is enter all its details into a table on the site and queue it up for checking https://gobrowser.com/proxy-checker/.