Best % uniqueness software
I'm currently looking for the best free uniqueness article software available. Let's say I write an article or buy an article and I wanna know if it's unique, where should I check. I mean I could copy line by line on Google and measure if it's unique but I will loose plenty of time.
Any ideas on which software can help me?
I would like it to be free too, if possibe.
Thanks
Alexis Barnabé