Necklace is a drawless connection game for two players: Red and Blue. It is played on the intersections (points) of an initially empty square grid (board). The top and bottom edges of the board are colored red; the left and right edges are colored blue.
A crosscut is a 2×2 area containing two diagonally adjacent red stones and two diagonally adjacent blue stones. A point is secluded if there is no free path along the lines of the board between that point and the edge of the board.
Red plays first, then turns alternate. On your turn, place a stone of your color on an empty point. After your placement, there must be no crosscuts and no secluded empty points on the board. Passing is not allowed, but, if you have no legal moves available, your turn is skipped.
You win if there is a chain of orthogonally connected stones of your color touching the two opposite board edges of your color.
To make the game fair, Blue will have the option, on their first turn only, to swap sides with Red instead of making a regular move.
—description from the designer