Bar replay rewinds a chart to a chosen date and reveals bars as if they were printing live. You place hypothetical entries, stops and targets and step forward.
It is the cheapest way to accumulate repetitions of a specific setup. Reviewing a hundred replayed examples of one pattern teaches more than a month of live trading at one trade a day, and it costs nothing.
Two honest limits. First, you usually know roughly what happened in that period, so hindsight-bias leaks in; replaying unfamiliar instruments and random dates helps. Second, replay ignores execution reality: no slippage, no partial fills, no emotional pressure. Treat results as a study of pattern frequency, not as a backtesting result or as proof of profitability.
Related: backtesting, paper-trading, hindsight-bias