The history of Bulls and Cows
CODEBREAK belongs to a very old family of games in which one player hides a secret and the other closes in on it through scored guesses. This page describes where the idea came from and how it reached a browser near you.
A game played on paper
Bulls and Cows is a two-player pencil-and-paper game. One player secretly writes down a number with four different digits. The other player guesses, and after each guess the first player reports two figures: the bulls, which are digits that are right and in the right place, and the cows, which are right digits in the wrong place. Play continues until the guesser names the number. Nobody can say for certain who first played it, and it has been enjoyed in many countries under many names. Its simple materials explain its long life: all you need are a pencil and a scrap of paper.
From paper to computers
The game was an early favourite for programmers. Around 1970 a version called Moo was written for a mainframe at the University of Cambridge, and the idea spread to other systems. A computer is a natural opponent for this game, because it can hold a secret perfectly and score guesses without error. The same reasoning also made the game a popular exercise for people learning to program, and for researchers who studied how few guesses a perfect player needs.
Mastermind
In 1970 an Israeli telecommunications expert, Mordecai Meirowitz, invented a board game with the same basic idea but coloured pegs in place of digits. It was sold by the British company Invicta Plastics from the early 1970s as Mastermind and became one of the best-selling games of its era. Mastermind and Bulls and Cows are cousins: a hidden code, guesses, and feedback that counts exact matches and misplaced matches. The main differences are the symbols (colours rather than digits) and the rules about repetition.
Daily puzzles
More recently, short daily puzzles turned into a habit for millions of people. A shared puzzle that changes once a day creates a small community, because everyone can compare experiences without spoiling the answer. CODEBREAK brings that format to the Bulls and Cows idea: one code per day, the same for everybody, eight tries, and a result you can share without giving anything away.
Why it still works
Bulls and Cows endures because it is easy to learn and surprisingly deep. The rules fit in a paragraph, yet playing well means tracking possibilities, noticing what each clue rules out and choosing guesses that teach you the most. If you want to try that approach yourself, read the strategy guide or head straight to today's CodeBreak.