PIOATool is the implementation of our compositional performance analysis techniques for PIOAs. The implementation currently consists of about 12,000 lines of code in the very high-level functional programming language Standard ML. We have done fairly extensive validation and performance tuning on the implementation, using example problems for which we know the correct answers, and we have obtained a significant amount of confidence in it. We are now beginning to try out the implementation on larger, more realistic examples of practical interest. A description of many of the algorithms used in PIOATool appeared in a paper presented at PAPM99.