Crack the Code

Crack the Code is a two-player logic-deduction race. You each hide a secret code made of digits. Then you both start guessing — at the same time, with no turns to wait for. Every guess comes back marked, and the marks are all you get. The first player to work out the other's code wins.

SET A CODE. CRACK THEIRS FIRST.

▸ QUICK DUEL
Get matched with a random opponent at the same difficulty, usually within seconds. If nobody else is queueing after ten seconds you get a server stand-in instead of a spinner — same rules, never sees your code, kept out of every leaderboard. Wins move your rating, and the leaderboard tracks the fewest guesses anyone has ever needed.

▸ PRIVATE ROOM
Create a six-character code and read it out to a friend. They type it in and you're duelling. No accounts, no friend requests, no waiting.

▸ DAILY CHALLENGE
One code a day per difficulty, the same one for every player on the planet, generated at midnight UTC. Twelve guesses. Ranked by fewest guesses first, then fastest time. Your attempt saves as you go, so you can put it down and come back.

▸ SOLO VS BOT
Four skill levels, from a bot that forgets what it was told to a Knuth minimax solver that never wastes a guess. You take turns — one guess each — so the scores are directly comparable. Works with no internet at all: on a plane, on the underground, anywhere.

TWO WAYS TO BE ANSWERED
• DETAILED — every digit of your guess is marked. Green means right digit, right place. Amber means that digit is in the code but somewhere else. Grey means it isn't in the code at all.
• CLASSIC — you are told only how many digits are exactly right and how many are misplaced. Never which. This is traditional Mastermind scoring, and working out which digit is which is the whole puzzle.

FOUR DIFFICULTY PRESETS
• Easy — 3 digits from 0-5, no repeats, Detailed. 120 possible codes.
• Normal — 4 digits from 0-9, no repeats, Detailed. 5,040 possible codes.
• Hard — 4 digits from 0-9, repeats allowed, Classic. 10,000 possible codes.
• Extreme — 5 digits from 0-9, repeats allowed, Classic. 100,000 possible codes.

A bigger haystack is not automatically harder. Extreme has ten times more codes than Hard but one extra digit in every answer, so a good solver needs about the same number of guesses. What makes those two hard is losing the per-digit marks.

A DEDUCTION HELPER, NOT A CHEAT
The duel screen counts how many codes are still consistent with everything you have been told, and gives you a digit grid to mark digits in or out as you work them out. It reveals nothing your own answers did not already imply — any player with a pencil could reach the same number. Switch it off in Settings if you would rather keep it all in your head.

NOBODY CAN CHEAT
On paper, the obvious cheat is to change your code once the other player gets close. That is impossible here. Your code is sent once and written down by our server, and no message exists that can change it afterwards. Your opponent's phone is only ever told the marks their own guesses earned. Both codes are revealed to both players at the same moment, when the duel ends. Guesses that break the rules are rejected by the server, so you cannot buy information with an illegal probe.

NO SIGN-UP, NO NONSENSE
• No account, no email, no password — pick a nickname and play
• No location, no contacts, no analytics SDK
• Solo vs Bot never contacts our server at all
• An ad when a game starts, never during one — or buy Premium once and never see another

TRACK YOUR GAME
Rating, win rate, and your personal best at every difficulty. Win within the number of guesses an optimal solver would need in the worst case and you earn a star — you cannot reliably do better than that.

Crack the Code is free to play, quick, and just as good against a stranger on the other side of the world as against the person sitting next to you. Premium is a single payment that removes ads for good — no subscription.

Set a code. Crack theirs first.