Building a Time-Travel Debugger involves addressing the challenges of deterministic and non-deterministic software behavior, akin to solving a complex game of Wordle. The debugger, Replay, capitalizes on the deterministic nature of software, requiring only the recording of specific library calls to enable accurate replaying of programs. However, issues arise with multi-threaded runtimes where inter-thread non-determinism becomes significant, necessitating the recording of lock orders to maintain behavior consistency during replay. The process of diagnosing these issues involves a strategic search for critical locks, using recording and replaying stack traces as clues, much like guessing words in Wordle to narrow down potential solutions. This blend of systematic recording and educated guessing is essential to improving Replay’s functionality, with the ultimate goal of making replayable runtimes a standard in software development.