A small down candle is swallowed whole by the next day's up candle. Sellers set the range, then buyers took all of it back and more — which is why it only counts as a signal if there was a downtrend to reverse.
Two sessions. The first closes lower than it opened. The second opens at or below that close, then closes above the first candle's open — its real body covers the previous body completely. The bigger the second body relative to the first, the more decisive the handover.
Context does the heavy lifting. The same two candles in the middle of a sideways drift are noise. The scan below only lists a stock if it was trading below its 20-day average before the pattern formed, so there was an actual decline for buyers to reverse.
Volume is the second filter. A day marked Confirmed traded at least 1.2× its 20-day average volume — the reversal had participation behind it, not just a thin book.
Most often when the stock is already deeply oversold and the engulfing candle is simply a short-covering bounce inside a continuing downtrend. Check RSI: a reading in the low teens rising to 25 is relief, not a turn.
It also fails on gap opens driven by news, where the wide body reflects a repricing rather than a shift in who is in control. And on illiquid counters, a single large order can manufacture the shape.
A pattern is a prompt to look closer, never a trade on its own. Traders who use these wait for the next session to hold above the engulfing candle's close before acting.