Polymarket Brier Score

Calculate prediction accuracy for any Polymarket address. Brier Score measures how close a trader's positions were to the actual outcomes — independent of PnL, position size, or trading strategy.

Why Brier Score?

PnL tells you who made money. Brier Score tells you who predicted correctly.

• High PnL + Poor Brier → Market maker or arbitrageur (earns spread, not predictions)
• Low PnL + Good Brier → Accurate predictor with small positions or conservative sizing
• High PnL + Good Brier → Skilled predictor who also sizes well — the real signal

Trigger

User asks about prediction accuracy, Brier score, prediction quality, forecasting skill, or "how accurate is this trader".

Background

The Brier Score is a standard metric in forecasting (used by Metaculus, Good Judgment Project, etc.).