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There are quite a few tools online, but one thing to keep in mind is you don't want to just go to some unknown website and start entering your actual passwords. After all, Acme Crime's website could have a password checker that welcomes you to give them all of your actual passwords. Microsoft has one that is interesting - it attempts to predict the next character. All of your browser log entries are encrypted on this site, by the way, before they are sent to MS's servers.