Crack a hidden 4-peg colour code in 10 tries. Read black/white feedback pegs after each guess. Six colours, classic rules, free in browser.
Pick a colour from the palette, then tap a slot in the active row to place a peg. Tap again with no colour selected to clear a slot. Fill four pegs and press Submit. Dark feedback = right colour right slot; light feedback = right colour wrong slot.
Mastermind is a two-player code-breaking puzzle invented by Israeli postmaster and telecommunications expert Mordecai Meirowitz in 1970. The commercial board game — with its iconic black-and-white plastic pegs — sold over fifty million copies in its first decade and became a staple in puzzle and logic curricula around the world.
Classic rules: one player picks a secret sequence of four coloured pegs, the other has up to ten guesses to crack it. After each guess the codemaker gives feedback — a *black* peg for every guess peg that matches both colour and position, a *white* peg for every guess peg whose colour appears in the code but in a different slot. No pegs at all means none of your colours feature.
Mastermind is a celebrated case study in deductive reasoning. Donald Knuth proved in 1977 that a five-guess strategy suffices for the standard 4×6 version, and the modern competitive scene still hunts for optimal openings. In this version the computer plays the codemaker — you get up to ten attempts to break a randomly generated four-peg code.
Yes. The codemaker may use the same colour multiple times, and our version follows the classic rule. That makes the search space 1,296 codes (6⁴) instead of just 360 unique permutations.
Dark (black) peg = one of your guess pegs is the right colour in the right slot. Light (white) peg = one of your guess pegs is a colour the code uses, but in a different slot. The two never double-count the same peg.
Ten. If you don't crack the code by the tenth row, the codemaker wins and the secret is revealed.
Yes. Knuth's 1977 algorithm guarantees a solution in five guesses or fewer for any 4-peg, 6-colour code — so ten is comfortable, even without machine-perfect play.
Yes. The codemaker scores black pegs by exact position. Swapping the order of two pegs can change the black/white split even if your colour selection is identical.
Mordecai Meirowitz, an Israeli postmaster and telecommunications expert, designed Mastermind in 1970. Invicta Plastics published it commercially in 1971 and it became one of the best-selling games of the 1970s.