Mastermind

What You Need

• A Mastermind set. That is a board with 10 rows of holes (some editions have 12), a hinged shield, code pegs in 6 colors, and small key pegs in two colors. Classic sets use black and white key pegs. Some newer sets use red and white pegs, or sliders. Same meaning.
• No set? Use pencil and paper. Write codes as four digits from 1 to 6.

Setup

1. Decide who makes the code first. Put the board between you with the four shielded holes facing the codemaker.
2. The codemaker picks 4 code pegs and puts them behind the shield. Any of the 6 colors, in any order. Repeats are allowed. Two reds, three reds, even four reds is legal.
3. The codebreaker sits on the other side and starts in the row nearest them.

How a Turn Works

1. The codebreaker places 4 code pegs in the next open row. That is a guess.
2. The codemaker scores the guess with key pegs in the small holes beside that row. One black peg for every guess peg that is the right color in the right position. One white peg for every guess peg that is the right color in the wrong position. Nothing for a color that is not in the code.
3. Key pegs go in any order. They never say which guess peg they refer to. Working that out is the game.
4. The codebreaker uses the feedback to build the next guess in the next row. Old rows stay where they are.
5. Repeat until a guess earns 4 black pegs, or the rows run out.

The Duplicates Rule

Each peg in the secret code can earn at most one key peg, and black beats white. Say the code holds one green. You guess two greens, one of them in the right spot. You get one black and no white. The second green earns nothing because there is no second green to match.

Another one. The code is red, blue, red, yellow. You guess green, red, red, white. Your third peg is red in the right spot, so one black. Your second peg is red in the wrong spot, and the code has a second red, so one white. Total: one black, one white.

Scoring

• The codemaker scores 1 point for every row the codebreaker used. Crack it in four rows and the codemaker gets 4.
• If the codebreaker never cracks it, the codemaker gets one point per row plus 1 bonus. On a 10-row board that is 11.
• If the codemaker gave wrong feedback, the classic rules replay that game and give the codebreaker 3 bonus points.
• Now swap roles and play again.

Winning

Play an agreed even number of games so each player makes the code the same number of times. Four or six is a normal match. Highest total wins. Scores go to the codemaker, so the better codebreaker is the one who gives away fewer points.

Two-Player Notes

• Mastermind is built for two. The roles are not equal, so swap after every game and play an even number.
• The codemaker's real job is accurate scoring. One wrong key peg ruins the game. Count blacks first, cover those pegs with a finger, then count whites.
• Check your board before you start. Ten rows is standard. Some editions give 12, which makes the no-crack bonus 13 instead of 11.
• Blanks: the classic rule book has a harder second game where the codemaker may leave holes empty. A blank counts as a seventh color. Agree before play, never mid-match.
• If one player stalls, set a 3 or 4 minute limit per guess.

Strategy Tips

• Open with two pairs, such as red, red, blue, blue. It tests two colors at once and gives position information too.
• Every guess must fit all feedback so far. If a guess is already ruled out, it wastes a row.
• A perfect player never needs more than 5 guesses. Donald Knuth proved that in 1977. Most people take 6 or 7.
• As codemaker, repeat a color. Codes with four different colors are the easiest to crack.

Variations

• Allow blanks. That is the classic rule book's second game, with 2,401 possible codes instead of 1,296.
• Pencil and paper: four digits from 1 to 6. Same feedback, no plastic.
• Super Mastermind: 5 pegs, 8 colors. A different board and a longer game.