This tool works using machine learning (neural networks). I trained a program by showing it over 200,000 ranked matches and had the program find patterns in the matches. The end result is a program that can fairly accurately predict the outcome of a match just from the champions being played.
To use the tool, fill in the columns with the champions on each team. Once filled, the tool will process your inputs and feed them through it's machine learning algorithm. The probability of each team winning will be displayed beneath the list of champions.
Remember, probabilities are not guarantees and many other factors influence who the final winner is. Don't tilt if your percent is low, and don't become complacent if the percent is high. Good luck!