Search engines like Google actively penalize IPs from known free proxy ranges. Using a free list for SEO rank tracking will give you wildly inaccurate results because Google serves different content to proxy IPs.

The script was designed to test the connections. It was the bottleneck. Usually, checking a few thousand proxies took hours. A million would take days.

ProxyBros : Maintains a large, filterable inventory of public IPs. Critical Risks of Free Proxy Lists

Watch for:

Websites like ProxyScrape and Spys.one offer free tiers. While they limit you to 100 or 500 at a time, power users write scripts to scrape the entire database over time, compiling their own million-proxy list.

If you are determined to use a free list, you cannot just load it into your scraper. You must build a pipeline.