Mastermind Guesser

A browser game where the computer guesses your secret Mastermind code. Plain HTML and JavaScript, no build step, no dependencies. Works on desktop and mobile.

How to play

1. Open index.html in a browser (or serve the folder with any static server).
2. Think of a secret code: 4 digits, each from 1 to 6, repeats allowed (1296 possible codes).
3. The computer shows a guess. Tell it how many bulls (right digit, right place) and cows (right digit, wrong place) it scored.
4. Repeat until it answers with 4 bulls. It never needs more than 5 guesses.

Enter the score by tapping the number chips under each field, or type both numbers and press Enter.

Impossible and dishonest answers

The game checks every answer before using it:

• Values outside 0–4, or bulls + cows above 4, are rejected.
• 3 bulls and 1 cow is rejected as logically impossible.
• An answer that no code could produce, given your earlier answers, is rejected with an explanation. Use Undo to step back and correct a previous answer.

Algorithm

The guesser uses Knuth's five-guess algorithm (1977):

1. Start with all 1296 codes as candidates.
2. For every possible guess, partition the candidates by the feedback each would return. The largest partition is that guess's worst case.
3. Play the guess with the smallest worst case (minimax). Ties prefer a guess that is itself still a candidate, then the lexicographically smallest.
4. Eliminate every candidate inconsistent with the real feedback and repeat.

Across all 1296 secrets this solves every code in at most 5 guesses, 4.476 on average. The implementation is a JavaScript port of the Zig Game struct from a companion multi-language solver (Python, V and Zig) and produces the same guess sequence as those versions.

Files

File	Purpose
index.html	Markup and styles, including the mobile layout and dark mode
script.js	Knuth solver (Game class) and the UI logic

License

MIT, see LICENSE.