Full policy: https://blunder.review/privacy

In short: the extension does nothing until you click it. It reads the address of the current tab to recognise a finished game on Chess.com or Lichess, keeps its settings in your browser's local extension storage, and — when you choose to review a game — sends that game's address to blunder.review. No browsing history, no analytics, no tracking, and nothing is collected from pages that are not a chess game you asked to review.