Out of sample is the real test
If overfitting is the disease, out of sample testing is the diagnosis. The idea is simple: judge the strategy on data it was never allowed to see.
Hold the last slice out
The trust strip under every result carries an OOS chip. The engine scores the last 30% of bars separately from the first 70% and grades whether the edge persisted late in the window. Nothing is fitted here, it is a plain split, but a strategy that only made money early in the window is exactly the kind of coincidence this catches. Hover the chip for the late slice's return and trade count.
Walk forward is the strict version
For the toughest test, open Robustness and Walk forward optimization, on Power and above. It optimizes a parameter on an in sample window and scores the winner only on the unseen window that follows, then rolls forward and does it again. That is the closest a backtest gets to how you would actually run and retune the strategy live.
Run it live
The strategy for this lesson, in plain English:
“Buy SOL when price crosses above the 50-day SMA, exit with a 10% trailing stop, on 1D, last 3 years.”
It opens already parsed, so you can read the rules before you spend a run.
Key takeaway
In sample performance is a hypothesis. Out of sample and walk forward are how you test it.
Terms in this lesson
Check yourself