Mastermind is a code-breaking game that helps develop deductive reasoning and logic by requiring players to deduce secret combinations of colours with minimal clues. After each of these chances, the creator of the code must reveal how many pegs are the correct colour in the correct location, or the correct colour in the incorrect location, or completely incorrect. With this little information, the code breaker must improve upon his previous guess to crack the code. Most Mastermind boards give players eight or 10 chances to correctly guess the code before requiring a forfeit.
Assign each player a role. One player must make the code and give clues, and the other must try to break it. Orient the board so that the shielded end faces the player making the code.
A sequence of four coloured pegs is chosen by the code maker and placed within the code shield. The sequence can incorporate one to four different colours. Most Mastermind boards include at least six different colours of pegs, which means that not all colours can be played at one time. The code breaker cannot see this arrangement.
The code breaker places four coloured pegs in the first row.
The code maker uses key pegs to show the correctness of the guessed pattern. A red key peg indicates that the colour is correct, and in the correct position. A white key peg indicates that the colour does occur in the sequence, but not in that position. If the colour does not appear at all in the sequence, the code maker does not use a key peg. The key pegs are not placed in any way that indicates which colour pegs the key pegs correspond to.
Game play continues by repeating steps 3 and 4 until the code breaker correctly guesses the code or all rows of the Mastermind board are filled without yielding a correct answer.
Score the game. The code maker receives one point for each incorrect guess made by the code breaker. If the code breaker can prove that the code maker provided incorrect feedback, the code breaker receives three points and the code maker forfeits all points. If the game is finished without a correct answer, the code maker receives 11 points.
Make the game easier by telling the code breaker what key pegs relate to which colour pegs. Improvise without the board by using coloured pieces of paper and hiding the secret code in a box. The code breaker then assembles pieces of paper in order, and the code maker provides feedback after each attempt. Complicate the game for more experienced players by allowing the code maker to use "blanks" in creating the code.