Gold Paper Trader came out of a simple frustration: you cannot learn to read a market at the speed the market moves. A live chart gives you a few setups a day, no rewind, and no way to ask what you should have done instead.
So this replays recorded days instead. Real 1-second gold futures bars, played back at whatever speed you want, with orders filled against the actual highs and lows of each second rather than an approximation. A stop that would have been hit is hit.
A demo account tells you what you made. This tells you why you lost. Every losing trade is diagnosed against the conditions at entry — the hourly trend, the strength of the level, the session, where RSI was — and turned into a recommendation: buy, sell, or stay out. Lose a hundred-trade session and it builds a training plan out of your own worst entries so you can replay them.
Bars are stored in MySQL and loaded once into memory, shared read-only across everyone using the app. Your session is a position in that shared data plus your own equity, orders and trades, checkpointed as you go — which is why you can shut the tab mid-trade and pick it up tomorrow.