ZigZag draws straight lines between turning points that exceed a threshold, producing a clean skeleton of swing-highs and swing-lows. It is the standard aid for counting waves, measuring retracements and eyeballing market-structure.
Its defining property is that the last leg is provisional. Until price moves far enough to confirm a new turning point, the most recent line can be redrawn, which means ZigZag repainting is not a bug but the definition of the tool.
This makes it worthless as a signal generator and dangerous in backtests, where using ZigZag points as entries produces spectacular and entirely fictional results. Use it to describe history, never to act in the present.
Related: repainting, swing-high, swing-low, market-structure, backtesting