Code-breaking puzzle. Guess the secret colour code from black and white pegs, with a live count of the codes still possible. Four difficulties, six modes
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Sudoku with a guarantee most generators skip: every puzzle is checked to have exactly one solution before you see it. Difficulty is measured by the techniques a puzzle needs, and hints say why a digit belongs where it does.
Minesweeper on the three standard boards or one of your own, with both first-click conventions offered by name: a safe square, or a safe square and its eight neighbours. Flags, question marks, chording and best times.
Brick breaker with continuous collision, so the ball never passes through a brick and bounces off the face it actually hits. Power-ups, boss levels, upgrades and achievements.
Your guess gets two black pegs and one white peg of feedback.
Guess + feedback
R G B Y → ●● (right colour+spot) ○ (right colour, wrong spot)
Deduction
Three of these four colours are in the code, one of them in the right place; the codes-left counter drops from 1,296
Black is right colour and right place, white is right colour and wrong place, counted from what is LEFT after the blacks have taken theirs, so a guess can never earn more pegs for a colour than the code contains. Combining that across guesses narrows the 1,296 possible codes, and the page shows how many are still consistent with everything you have been told. Knuth proved in 1976 that five guesses always suffice for four pegs from six colours; the Code Maker AI uses his rule and averages 4.48.
Crack a secret color code using logic and deduction. After each guess, you receive feedback telling you how many colors are correct and how many are in the right position. Can you break the code within the allowed attempts?
Each game is a structured deduction exercise that sharpens analytical thinking.
Forming hypotheses and testing them against feedback mirrors real scientific inquiry.
The elimination logic in Mastermind maps directly to debugging and constraint-solving skills.
Race a friend to see who can crack the code in fewer guesses.
Mastermind rewards systematic thinking, and this version makes "narrows the possibilities" a number: a counter shows how many codes are still consistent with every answer you have been given, out of 1,296 for the standard four pegs from six colours. Two things decide whether a Mastermind is right, and both are about repeated colours. The pegs are counted in two passes: black pegs for the exact matches, then white pegs from what is LEFT on both sides, so a guess never gets more pegs for a colour than the code contains. Super mode's per-position rings are derived from the same calculation, so the two displays can never say different things. And the code itself is drawn as a shuffle rather than by redrawing a colour until it is new, which is what lets No Duplicates mode work at any length and palette. Knuth proved in 1976 that any of the 1,296 codes can be cracked in at most five guesses; the AI in Code Maker mode uses his minimax rule and needs 4.48 on average.
The default is 10 attempts, but you can adjust the difficulty for more or fewer.
Black peg = correct color in the correct position. White peg = correct color but wrong position. No peg = that color is not in the code (for that slot).
For the standard four pegs from six colours, yes: Knuth proved in 1976 that five guesses are always enough, and the default limit is ten. Harder settings have larger code spaces, so the limit is tighter relative to the search.
The pegs are counted in two passes. Black pegs are taken first and each one uses up that colour on both sides; white pegs then come from what is left. So guessing three of a colour when the code holds two can never earn three pegs for it.
How many of the possible codes still fit every answer you have been shown. It is a fact about the feedback, so you can check it, and it goes to one exactly when the code is forced.
The game runs entirely in your browser. No account is needed and no gameplay data is collected.