This script will tell you if a die is biased or not.

In order for the statistics to work properly, you'll need to roll your die enough times for each result to be able to occur at least 5 times. So, for example, if you want to test a d6 you'll need to roll it at least 6 x 5 = 30 times. If you want the assessment to be more accurate, then use a number greater than 5; the higher this number ("E" in the form below), the better.