The 5 signs your backtest is lying.
Most strategies don't fail in the market — they fail in the backtest, quietly, before a dollar is risked. Learn the five ways a beautiful backtest deceives you, and the exact check that catches each one.
Five lies. Five checks.
The future peek
Look-ahead bias — when your rule quietly used information that didn't exist yet, and how one question exposes it.
The free trades
Why ignoring spread, commission and slippage turns losing strategies into paper winners — and the cost test to run.
The thin sample
Why 20 trades at 70% means almost nothing — the coin-flip math that keeps you humble.
The tuned curve
Curve-fitting: test twenty variants and one shines by luck. How to know if yours is the lucky one.
The missing exam
Out-of-sample testing — the one discipline that separates a track record from a memory.
Then go deeper
Ready to build one honestly? The Algo Building Starter Kit is the full 25-lesson path — no coding background required.