Crack a monoalphabetic substitution cipher (cryptogram) by hand or let a hill-climbing solver guess the key from English letter and bigram frequencies. Type in any cell to assign a plaintext letter; locked cells stay fixed during auto-solve. Works on any cipher where each letter is replaced by a unique other letter.
Type a plaintext letter under each cipher letter. Empty cells stay ?. Locked (green) cells aren't changed by the auto-solver.
English letter order (high→low): E T A O I N S H R D L C U M W F G Y P B V K J X Q Z. The most common cipher letter is usually E; the next two are usually T and A.
The solver starts from the frequency-seeded key (most common cipher letter → E, next → T, and so on), then repeatedly swaps two plaintext letters in the key. After each swap it scores the candidate plaintext using the log-probability of English bigrams (LL, TH, HE, IN, ER…). If the swap raises the score, it's kept; otherwise it's reverted. After a few thousand swaps with periodic random restarts, the score plateaus on a fluent English key for messages longer than ~80 letters. Short cryptograms (under 50 letters) rarely have enough signal to fully crack — use the manual keymap above to fix obvious words like "THE" and "AND", lock those cells, and rerun.
Substitution ciphers preserve word boundaries, letter repetition, and punctuation, so once you spot a three-letter word that appears often, it's almost certainly THE. A doubled letter at the end of a word is usually LL, EE, SS, or OO. Apostrophe-S patterns give away 'S and 'T.