All 25 shifts (brute force)
Each row decodes your text by moving each symbol back that many places. The highlighted row looks most like English.
| Shift | Decoded text | Copy |
|---|---|---|
| 1 | Vjg ugetgv oggvkpi ku cv pqqp pgct vjg qnf dtkfig. | |
| 2 | Uif tfdsfu nffujoh jt bu oppo ofbs uif pme csjehf. | |
| 3 * | The secret meeting is at noon near the old bridge. | |
| 4 | Sgd rdbqds lddshmf hr zs mnnm mdzq sgd nkc aqhcfd. | |
| 5 | Rfc qcapcr kccrgle gq yr lmml lcyp rfc mjb zpgbec. | |
| 6 | Qeb pbzobq jbbqfkd fp xq kllk kbxo qeb lia yofadb. | |
| 7 | Pda oaynap iaapejc eo wp jkkj jawn pda khz xnezca. | |
| 8 | Ocz nzxmzo hzzodib dn vo ijji izvm ocz jgy wmdybz. | |
| 9 | Nby mywlyn gyyncha cm un hiih hyul nby ifx vlcxay. | |
| 10 | Max lxvkxm fxxmbgz bl tm ghhg gxtk max hew ukbwzx. | |
| 11 | Lzw kwujwl ewwlafy ak sl fggf fwsj lzw gdv tjavyw. | |
| 12 | Kyv jvtivk dvvkzex zj rk effe evri kyv fcu sizuxv. | |
| 13 (ROT13) | Jxu iushuj cuujydw yi qj deed duqh jxu ebt rhytwu. | |
| 14 | Iwt htrgti bttixcv xh pi cddc ctpg iwt das qgxsvt. | |
| 15 | Hvs gsqfsh asshwbu wg oh bccb bsof hvs czr pfwrus. | |
| 16 | Gur frperg zrrgvat vf ng abba arne gur byq oevqtr. | |
| 17 | Ftq eqodqf yqqfuzs ue mf zaaz zqmd ftq axp ndupsq. | |
| 18 | Esp dpncpe xppetyr td le yzzy yplc esp zwo mctorp. | |
| 19 | Dro combod woodsxq sc kd xyyx xokb dro yvn lbsnqo. | |
| 20 | Cqn bnlanc vnncrwp rb jc wxxw wnja cqn xum karmpn. | |
| 21 | Bpm amkzmb ummbqvo qa ib vwwv vmiz bpm wtl jzqlom. | |
| 22 | Aol zljyla tllapun pz ha uvvu ulhy aol vsk iypknl. | |
| 23 | Znk ykixkz skkzotm oy gz tuut tkgx znk urj hxojmk. | |
| 24 | Ymj xjhwjy rjjynsl nx fy stts sjfw ymj tqi gwnilj. | |
| 25 | Xli wigvix qiixmrk mw ex rssr riev xli sph fvmhki. |
How to use
Paste your ciphertext
Replace the sample in the Ciphertext box with your message and pick an Alphabet if it is not plain A to Z. The Output box and the brute force table update as you type. Try sample restores the example.
Use the likely shift or set one
With about 20 or more letters, a most likely shift appears. Click Decode with shift to apply it, or drag the Shift slider yourself. Choose Encode to shift letters forward instead.
Copy the result
Click Copy above the Output box, use the Copy button on any row of the brute force table, or download every row as CSV or .txt. The highlighted row is the one that looks most like English.
Why Caesar Cipher Decoder
- Decodes without the key by trying every shift at once, with CSV export.
- Ranks shifts by English letter frequency and suggests the likely one.
- A to Z, digits, classical Latin, ASCII or a custom alphabet.
- Decode and Encode modes, and a one-click ROT13 button.
How to crack a Caesar cipher without the key
A Caesar cipher on the normal alphabet has only 25 useful keys, so the simplest attack is brute force: decode with every shift and look for the one that reads as English. The brute force table does exactly that, for whichever alphabet you pick.
For longer messages there is a faster way called frequency analysis. English uses some letters far more than others, with E, T, A and O at the top and Q, X and Z at the bottom. A Caesar shift moves every letter by the same amount, so the pattern of common and rare letters survives. The tool counts the letters in each of the 25 decodings and scores how far they are from normal English using a chi-squared test. The lowest score becomes the suggested shift.
Frequency analysis needs enough letters to work. Below about 20 letters the tool does not suggest a shift, because a short phrase can easily have an unusual mix of letters.
Other alphabets change the number of keys: 35 with digits added, 22 for the classical Latin alphabet and 93 for printable ASCII.
Every shift of HELLO
This table shows the word HELLO encoded with each shift from 1 to 25. To decode any of these, choose Decode and set the slider to the number in the first column.
| Shift | HELLO becomes | Shift | HELLO becomes |
|---|---|---|---|
| ROT1 | IFMMP | ROT14 | VSZZC |
| ROT2 | JGNNQ | ROT15 | WTAAD |
| ROT3 | KHOOR | ROT16 | XUBBE |
| ROT4 | LIPPS | ROT17 | YVCCF |
| ROT5 | MJQQT | ROT18 | ZWDDG |
| ROT6 | NKRRU | ROT19 | AXEEH |
| ROT7 | OLSSV | ROT20 | BYFFI |
| ROT8 | PMTTW | ROT21 | CZGGJ |
| ROT9 | QNUUX | ROT22 | DAHHK |
| ROT10 | ROVVY | ROT23 | EBIIL |
| ROT11 | SPWWZ | ROT24 | FCJJM |
| ROT12 | TQXXA | ROT25 | GDKKN |
| ROT13 | URYYB |
A short history: Julius Caesar and ROT13
The cipher is named after Julius Caesar. The Roman historian Suetonius wrote that Caesar protected private letters by replacing each letter with the one three places further along the alphabet, so a shift of 3. At a time when few people could read at all, and fewer still knew the trick, even this simple scheme kept casual readers out.
Much later, a shift of 13 became popular on Usenet discussion groups in the 1980s. ROT13 was used to hide joke punchlines and spoilers so that nobody read them by accident. Because 13 is half the alphabet, the same step both hides and reveals the text, which made it easy to build into newsreader software. It still turns up today in puzzles, programming exercises and capture the flag contests, where this decoder handles it at slider position 13.