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Caesar Cipher Decoder with All-Shift Ranking

Paste Caesar ciphertext and enter its shift, or inspect all ranked candidates below the result. This example decodes PHHW DW WKH ROG PLOO using shift 3. The ranking tries every nonzero shift of the selected alphabet; on A to Z that is 25 candidates. Lower chi-squared is closer to English letter frequency, but short messages and other languages can rank incorrectly. Read the candidates and use a plausible shift to decode the complete text.

Plain textCaesar, shift 3
MEET AT THE OLD MILL

decode A = 0 to Z = 25, wrapping after Z; case kept; spaces, digits and punctuation pass through

plainABCDEFGHIJKLM
cipherDEFGHIJKLMNOP
plainNOPQRSTUVWXYZ
cipherQRSTUVWXYZABC
  1. P15 - 3 = 12, M
  2. H7 - 3 = 4, E
  3. H7 - 3 = 4, E
  4. W22 - 3 = 19, T
  5. D3 - 3 = 0, A
  6. W22 - 3 = 19, T
  7. W22 - 3 = 19, T
  8. K10 - 3 = 7, H
  9. H7 - 3 = 4, E
  10. R17 - 3 = 14, O
  11. O14 - 3 = 11, L
  12. G6 - 3 = 3, D

and 4 more, worked the same way

encode shift forward 3 to encode again

Shift
Alphabet
Method
Caesar, shift 3
Letters shifted
16
Passed through
4
Encode
shift forward 3 to encode again

Every letter moves the same number of places along the alphabet and wraps round after the last one. Type your own alphabet to shift digits or symbols as well.

Every shift, ranked

All 25 shifts were undone. For each result the letters A to Z are counted and compared with standard English letter frequencies by a chi-squared score, and lower is closer to English. The ranking is an estimate, not a solution: read down until a line makes sense.

  • Shift 3rank 1, score 24.0
    MEET AT THE OLD MILL
  • Shift 22rank 2, score 36.1
    TLLA HA AOL VSK TPSS
  • Shift 14rank 3, score 71.9
    BTTI PI IWT DAS BXAA
  • Shift 19rank 4, score 87.0
    WOOD KD DRO YVN WSVV
  • Shift 2rank 5, score 106.4
    NFFU BU UIF PME NJMM
  • Shift 9rank 6, score 109.7
    GYYN UN NBY IFX GCFF
  • Shift 7rank 7, score 130.0
    IAAP WP PDA KHZ IEHH
  • Shift 11rank 8, score 132.7
    EWWL SL LZW GDV EADD
  • Shift 21rank 9, score 134.5
    UMMB IB BPM WTL UQTT
  • Shift 4rank 10, score 176.9
    LDDS ZS SGD NKC LHKK
  • Shift 1rank 11, score 200.9
    OGGV CV VJG QNF OKNN
  • Shift 20rank 12, score 210.5
    VNNC JC CQN XUM VRUU
  • Shift 12rank 13, score 234.2
    DVVK RK KYV FCU DZCC
  • Shift 18rank 14, score 296.6
    XPPE LE ESP ZWO XTWW
  • Shift 10rank 15, score 407.3
    FXXM TM MAX HEW FBEE
  • Shift 5rank 16, score 429.5
    KCCR YR RFC MJB KGJJ
  • Shift 16rank 17, score 467.2
    ZRRG NG GUR BYQ ZVYY
  • Shift 13rank 18, score 530.5
    CUUJ QJ JXU EBT CYBB
  • Shift 25rank 19, score 666.0
    QIIX EX XLI SPH QMPP
  • Shift 15rank 20, score 778.5
    ASSH OH HVS CZR AWZZ
  • Shift 6rank 21, score 832.6
    JBBQ XQ QEB LIA JFII
  • Shift 8rank 22, score 837.8
    HZZO VO OCZ JGY HDGG
  • Shift 23rank 23, score 878.3
    SKKZ GZ ZNK URJ SORR
  • Shift 24rank 24, score 984.3
    RJJY FY YMJ TQI RNQQ
  • Shift 17rank 25, score 998.6
    YQQF MF FTQ AXP YUXX

Only 16 letters to score. Under 40 letters one unusual word can reorder the list, so read every row.

Textbook checks, one per method

Each row is worked by the same code as the stage above. Load puts it in the workbench with its keys.

  • Caesar, shift 3ABCXYZ
    DEFABC
  • Keyword KRYPTOSKNOWLEDGE IS POWER
    DGHVETPST BM IHVTL
  • Polybius 5 x 5, I and J share cell 24JAM
    24 11 32, which decodes as IAM
  • A1Z26, numbers separated by spaces1 26
    AZ
  • Nihilist, square ZEBRAS, key RUSSIANDYNAMITE WINTER PALACE
    37 106 62 36 67 47 86 26 / 104 53 62 77 27 55 / 57 66 55 36 54 27
  • Book cipher, a 40-word reference text3 17 52
    error: word 52 is outside the 40-word reference, and nothing is guessed
  • One-time pad, key XMCKLHELLO
    EQNVZ
Puzzles and teaching, not secrets. These are historical and puzzle ciphers. Caesar has only 25 shifts on A to Z, so the ranked list that Decode shows reads most messages without the key, and keyword, Polybius and A1Z26 text gives way to letter counting. The one-time pad mode shows the arithmetic of a key you type and nothing more: this tool does not make keys and makes no claim that a message stays secret.
Accuracy. Each method follows the convention shown beside it: Caesar shifts count from 0 at the first letter of the alphabet and wrap after the last, the 5 x 5 Polybius and Nihilist squares give I and J one cell, A1Z26 reads 1 26 as AZ, and a book number outside your reference is an error, never a guess. The ranked list of Caesar shifts is an estimate from English letter frequency. These are historical and puzzle ciphers, not modern secure encryption, and the one-time pad mode only shows the arithmetic of the key you type, with no claim that it keeps a message secret.

Common questions

Can I decode without the key?
For Caesar, the small shift space can be inspected directly. Every nonzero shift is listed and ranked. The unchanged input is the zero-shift candidate. This is an English-frequency estimate, not proof of plaintext or a general cipher solver.
What does a negative shift mean?
A shift of -3 is equivalent to 23 on A to Z. Encoding adds the shift; decoding subtracts it. Both wrap after the final alphabet character.
Can I decode a Caesar cipher containing numbers?
Yes, when the original cipher shifted an alphabet containing digits. Enter that same alphabet in the same order. A to Z leaves digits unchanged; A to Z followed by 0 to 9 shifts all 36 symbols.

Each method follows the convention shown beside it: Caesar shifts count from 0 at the first letter of the alphabet and wrap after the last, the 5 x 5 Polybius and Nihilist squares give I and J one cell, A1Z26 reads 1 26 as AZ, and a book number outside your reference is an error, never a guess. The ranked list of Caesar shifts is an estimate from English letter frequency. These are historical and puzzle ciphers, not modern secure encryption, and the one-time pad mode only shows the arithmetic of the key you type, with no claim that it keeps a message secret.