Account sharing

Account sharing means an account is used by more than one person. In competitive chess, the important case is allowing someone else to play games under the account holder's profile, name, or competitive strength rating. That makes it unreliable to know who produced the results and can distort pairings, ratings, prizes, or fair-play checks, meaning checks that the competition's permitted-play rules are being followed.

Rules vary by platform. Chess.com prohibits letting another person play on your account. Lichess also prohibits account sharing in general but lists narrow, transparent exceptions for educational activities, streaming, or hand-and-brain games, a cooperative format in which two people share move decisions, subject to disclosure conditions. The Online Arena of the International Chess Federation (FIDE) prohibits substitute players from sharing an account in order to play games.

It is not the same as smurfing, where one person competes through an account that hides or understates their strength. It also does not require engine assistance: an account can be shared even if both users play without software. In some cases it can be used for artificially inflated results, such as when a much stronger player takes over another person's account to win games.