Select the Toolbox on the top menu, and then select the Proxy Tester. Once you input your proxies in the specified format, the option to select a target site to test will be displayed. You can test Adidas/Yeezy Supply, Footsites (US/EU), Supreme, Shopify, or a Custom Site.
After testing on your specified site, you will be able to view how many proxies are working and the average speed. You will also be able to see each proxy's speed and if the test was successful or not.
Clicking Clear Bad Proxies will remove all the proxies that tested bad from the list and allow you to copy only the ones that work.