Mastermind

Mastermind was invented in 1970 by Mordecai Meirowitz and became a major code-breaking board game after Invicta Plastics released it in the early 1970s. The idea descends from Bulls and Cows: one player hides a code, and the other uses feedback to narrow it down. Online, the computer sets the hidden pattern. Each guess gives exact-position and wrong-position clues. The challenge is information. A good guess does not just try to win; it splits the remaining possibilities. Start guessing and decode the pattern.

1. Choose a sequence of colored pegs for your first guess.
2. Submit the guess to receive feedback.
3. A black peg usually means one color is correct and in the correct position.
4. A white peg usually means one color is correct but in the wrong position.
5. Use the feedback to remove impossible codes.
6. Win by guessing the exact hidden code before the turn limit runs out.

• The common game uses four positions and six colors.
• Colors may repeat unless the selected rule set says otherwise.
• Feedback does not tell you which exact peg earned each clue.
• Black feedback counts exact matches.
• White feedback counts color matches in the wrong positions.
• Each new guess should fit all earlier feedback.

• Start with a balanced test such as two pairs of colors. It gives repeat information early.
• Separate color discovery from position testing. First learn which colors exist, then place them.
• Keep a list of impossible colors after zero-feedback guesses.
• Use Knuth-style thinking: choose guesses that reduce the largest remaining group of possible codes.
• Do not ignore duplicate colors. If a guess gets fewer clues than expected, one repeated color may be absent.

• Bulls and Cows: The older number-based code-breaking game that inspired Mastermind.
• Word Guess: Uses similar positional feedback with letters instead of colors.
• Super Mastermind: Adds more positions or colors for a larger search space.
• 6 Pegs: Six positions with eight colors. The largest search space for expert code-breakers.

• Every clue reduces the mystery.
• The game rewards organized note-taking.
• Short rounds still allow deep deduction.
• It feels fair because all feedback follows a strict rule.

Play Mastermind online for free. Test colors, interpret feedback pegs, and narrow the hidden code with each guess.

Mastermind is pure deduction in a small board. Make guesses that teach you something, track every clue, and let the possible codes shrink until one answer remains.

• Mastermind - Wolfram MathWorld
• Mastermind Board Game History