Mastermind — free browser game

Crack the computer's hidden 4-peg colour code in as few guesses as possible. Easy mode uses 6 colours, Hard uses 8 — colours can repeat in the secret. Click a slot in the active row to open the palette and pick a colour; click again to change or use × to clear. With all four slots filled, hit Check (or Enter) to submit. Feedback appears on the right as two kinds of pegs: a filled black peg means a correct colour in the correct position, an empty white peg means a correct colour in the wrong position. The order of the feedback pegs doesn't map to slot positions — only the counts matter. Crack the code in 10 attempts to win; run out and the secret is revealed. Tip: spend the first two guesses sweeping different colour groups to find which colours are in the code, then hold those colours fixed and shuffle their positions to pin them down. R starts a new round.