TLC is a model checker for specifications written in TLA+. TLA+ is a specification language based on TLA, the Temporal Logic of Actions. See the TLA web page for general information about TLA. You will most likely want to use TLC from the TLA Toolbox. Downloading the Toolbox brings with it the latest version of all the TLA+ tools, including TLC. How to write TLA+ specifications is explained in Specifying Concurrent Systems , which also describes TLC. However, it doesn’t tell you how to use the Toolbox.