Crack the hidden rule.
CIPHER is a puzzle about noticing. Every round shows you three example pairs — an input and what it turns into. Somewhere behind them is one hidden rule: reverse the word, shift the letters, count something, swap something. Your job is to induce the rule from the examples, then prove you've got it by answering a brand-new test input. Unlimited guesses; a hint (a fourth example) is always available, and it only costs you the clean crack.
Every day there are four puzzles — the same four for every player in the world — ramping from a gentle warm-up to a genuinely tricky finale. Crack all four and your result grid (🟩 clean, 🟨 with a hint, 🟥 revealed) is yours to share, spoiler-free. Practice mode is endless if one round a day isn't enough.
The rules aren't arbitrary — most of them are miniature versions of real techniques from cryptography, wordplay, and mathematics. Crack a Caesar shift and the game tells you how Caesar ciphers actually work. Crack a vowels-removed round and you'll learn that the earliest alphabets wrote consonants only. Everything you crack is collected in your Rules Cracked library, family by family, with the real story behind each one.
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Found a rule that feels ambiguous? Have a great idea for a new rule family? We'd genuinely like to hear it — see the Contact page.