Guess the secret row of colours, read the feedback pegs, and tighten your deductions until you crack the code.
The computer hides a secret sequence of coloured pegs. Each turn you submit a full guess and receive feedback: a black peg for every peg that is the right colour in the right spot, and a white peg for every peg that is the right colour in the wrong spot. The feedback pegs are unordered, so a black peg does not tell you which slot it refers to. Use the clues to deduce the code before your guesses run out.
The game usually sold as Mastermind was invented in 1970 by Mordecai Meirowitz, an Israeli postmaster and telecommunications expert. Major toy companies turned it down; it was picked up at the Nuremberg toy fair by Invicta Plastics of Leicester, refined by their founder Edward Jones-Fenleigh, and released in 1971–72.
It was not new so much as re-packaged. The underlying game is bulls and cows, a pencil-and-paper guessing game considerably older than the plastic pegs — which is the same game you will find elsewhere in this catalogue under its own name.
Computers reached it before the toy trade did. A version ran on Cambridge University's Titan in the 1960s under the name MOO, written by Frank King, and implementations followed on time-sharing systems and Unix — unsurprising for a game that is really an exercise in narrowing a search space by the fewest questions.
Codebreaker is a classic code-breaking deduction game of hidden colours and logical feedback. This is an original, free browser version with daily and practice modes and adjustable difficulty, no download or sign-up required.