Annualized mean excess return over return volatility. Above 1 is good; above 3 usually means a bug.

Sharpe with only downside deviation in the denominator.

Worst peak-to-trough decline of the equity curve.

Gross profit over gross loss.

Trade P&L in units of initial risk.

Worst and best unrealized excursion while open.

Train on a rolling window, test on the next unseen one.

Out of sample: data the parameters never saw.

A naive forecast. If a learned model cannot beat these, it has not earned its inference cost.