Mastermind is a guessing game where you play against the computer. The computer creates a secret code made up of four colored circles. The colors can be different from each other and can repeat only once.

Your job as the player is to guess the secret code. You do this by clicking on the coloured circles in the pink rectangle. The computer will then give you clues to help you figure out the code. These clues come in the form of red and white circles on the right side of the board. A red circle means that one of the colors you put in is in the right position and a white circle means that a color you put in is in the secret code, but you don't have it in the right position yet.