There is. Flyertalk.com.

I have heard rumors of a ST RTW tool but I've never actually seen it and it is pretty much impossible to find anything on their website these days, so I haven't even tried looking recently.

But if you post it here (preferably in the RTW sticky at the top of the forum) folks will be happy to help you validate it. You can also use the Great Circle Mapper tool to check on some backtracking issues.