What is a cryptogram?

A cryptogram is a puzzle where a message is encoded by substituting each letter with a different letter or symbol. The most common type is a simple substitution cipher, where each letter maps consistently to exactly one other letter throughout the message.

Solving strategies

Letter frequency: in English, E, T, A, O, I, N are the most common letters. The most frequent cipher letter is likely E.
Single-letter words: only "I" and "a" are single-letter English words.
Common short words: THE, AND, IT, OF, IS, BE are very common 2–3 letter combos.
Double letters: LL, SS, EE, TT, and OO are the most common doubled letters.

Full frequency analysis table

Frequency analysis is the cornerstone of breaking simple substitution ciphers. English letter frequencies in order (percentage of all letters in typical English text):

Letter	Frequency
E	12.7%
T	9.1%
A	8.2%
O	7.5%
I	7.0%
N	6.7%
S	6.3%
H	6.1%
R	6.0%
D	4.3%
L	4.0%
U	2.8%
C, M, W, F, G, Y, P, B	1.5–2.5% each
V, K, J, X, Q, Z	<1% each

History of cryptograms

Edgar Allan Poe was fascinated by ciphers and published The Gold-Bug (1843), a short story centered on solving a substitution cipher to find buried treasure. During World War I and II, substitution ciphers were used in military communications before more sophisticated methods (like the Enigma machine) replaced them. The Zodiac Killer's 1969–1970 cryptograms became infamous unsolved puzzles; the 340-character cipher (Z340) was finally cracked in 2020 by amateur codebreakers using modern computational techniques.

Common two-letter words

Two-letter words
OF, TO, IN, IS, IT, BE, AS, AT, SO, WE, HE, BY, OR, ON, DO, IF, ME, MY, UP, AN, GO, NO

When solving, look for frequently repeated two-letter sequences - they are almost always one of these words. Identifying just one or two of these anchors opens up the rest of the cipher.