If you have aymans http post plugin there is a proxy check function,if not you can make a function to say navigate to a site,or better yet a script SRC ,like the SRC for jquerry,so it is fast not loading an entire page,if document text contains "jquery" then start,if contains 404 eror(or whatever that URL error is,then reject,ask user to input another proxy,or continue without proxy You could also use a headless browser in new browser window for even faster check https://code.jquery.com/jquery-1.10.2.js