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Caesar Cipher Decoder,
crack any shift in seconds.
Use this free Caesar cipher decoder to encode a message, decode it with a known shift, or crack it by brute force. When the shift is unknown, all 25 possibilities are tried and ranked by how much like English they read, using letter frequencies and a word list.
Interactive
Caesar Cipher Decoder
What do you want to do?
Unknown shift: all 25 are tried and ranked by how much like English they read.
Most likely shift
7
The best shift reads clearly like English and beats the runner-up by a wide margin. Ranking is a statistical guess, not a proof.
All 25 shifts, best first
Ranked by how English they look
Loading the full word list… using a small built-in one meanwhile
- 1
Shift 7words 81% · χ² 21.3
Meet me at the old stone bridge at nine. Bring the map, and tell no one.
- 2
Shift 13words 11% · χ² 244.2
Gyyn gy un nby ifx mnihy vlcxay un hchy. Vlcha nby guj, uhx nyff hi ihy.
- 3
Shift 19words 11% · χ² 321.5
Assh as oh hvs czr ghcbs pfwrus oh bwbs. Pfwbu hvs aod, obr hszz bc cbs.
- 4
Shift 3words 11% · χ² 816.7
Qiix qi ex xli sph wxsri fvmhki ex rmri. Fvmrk xli qet, erh xipp rs sri.
- 5
Shift 20words 9% · χ² 490.0
Zrrg zr ng gur byq fgbar oevqtr ng avar. Oevat gur znc, naq gryy ab bar.
- 6
Shift 18words 7% · χ² 254.2
Btti bt pi iwt das hidct qgxsvt pi cxct. Qgxcv iwt bpe, pcs itaa cd dct.
- 7
Shift 14words 6% · χ² 1412
Fxxm fx tm max hew lmhgx ukbwzx tm gbgx. Ukbgz max fti, tgw mxee gh hgx.
- 8
Shift 6words 4% · χ² 254.8
Nffu nf bu uif pme tupof csjehf bu ojof. Csjoh uif nbq, boe ufmm op pof.
- 9
Shift 15words 4% · χ² 287.2
Ewwl ew sl lzw gdv klgfw tjavyw sl fafw. Tjafy lzw esh, sfv lwdd fg gfw.
- 10
Shift 25words 4% · χ² 546.7
Ummb um ib bpm wtl abwvm jzqlom ib vqvm. Jzqvo bpm uix, ivl bmtt vw wvm.
- 11
Shift 16words 4% · χ² 587.8
Dvvk dv rk kyv fcu jkfev sizuxv rk ezev. Sizex kyv drg, reu kvcc ef fev.
- 12
Shift 23words 4% · χ² 791.2
Wood wo kd dro yvn cdyxo lbsnqo kd xsxo. Lbsxq dro wkz, kxn dovv xy yxo.
- 13
Shift 17words 4% · χ² 1025
Cuuj cu qj jxu ebt ijedu rhytwu qj dydu. Rhydw jxu cqf, qdt jubb de edu.
- 14
Shift 21words 4% · χ² 3319
Yqqf yq mf ftq axp efazq ndupsq mf zuzq. Nduzs ftq ymb, mzp fqxx za azq.
- 15
Shift 9words 0% · χ² 355.2
Kccr kc yr rfc mjb qrmlc zpgbec yr lglc. Zpgle rfc kyn, ylb rcjj lm mlc.
- 16
Shift 24words 0% · χ² 563.0
Vnnc vn jc cqn xum bcxwn karmpn jc wrwn. Karwp cqn vjy, jwm cnuu wx xwn.
- 17
Shift 8words 0% · χ² 567.3
Ldds ld zs sgd nkc rsnmd aqhcfd zs mhmd. Aqhmf sgd lzo, zmc sdkk mn nmd.
- 18
Shift 5words 0% · χ² 587.0
Oggv og cv vjg qnf uvqpg dtkfig cv pkpg. Dtkpi vjg ocr, cpf vgnn pq qpg.
- 19
Shift 22words 0% · χ² 633.9
Xppe xp le esp zwo dezyp mctorp le ytyp. Mctyr esp xla, lyo epww yz zyp.
- 20
Shift 11words 0% · χ² 947.0
Iaap ia wp pda khz opkja xnezca wp jeja. Xnejc pda iwl, wjz pahh jk kja.
- 21
Shift 4words 0% · χ² 1069
Phhw ph dw wkh rog vwrqh eulgjh dw qlqh. Eulqj wkh pds, dqg whoo qr rqh.
- 22
Shift 2words 0% · χ² 1441
Rjjy rj fy ymj tqi xytsj gwnilj fy snsj. Gwnsl ymj rfu, fsi yjqq st tsj.
- 23
Shift 10words 0% · χ² 1477
Jbbq jb xq qeb lia pqlkb yofadb xq kfkb. Yofkd qeb jxm, xka qbii kl lkb.
- 24
Shift 1words 0% · χ² 1622
Skkz sk gz znk urj yzutk hxojmk gz totk. Hxotm znk sgv, gtj zkrr tu utk.
- 25
Shift 12words 0% · χ² 2737
Hzzo hz vo ocz jgy nojiz wmdybz vo idiz. Wmdib ocz hvk, viy ozgg ij jiz.
Letters were swapped at random instead of shifted? That is a general substitution cipher: try the Cryptogram Solver.
Field guide
How the Caesar Cipher Decoder works.
The Caesar cipher is one of the oldest ciphers there is. Each letter of the message is replaced by the letter a fixed number of places further along the alphabet, wrapping from Z back to A. The Roman historian Suetonius describes Julius Caesar writing private letters with a shift of three, so A became D, B became E and so on. The number of places is called the shift, or the key.
Encoding and decoding with a known shift
Choose Encode or Decode, set the shift from 0 to 25, and the result updates as you type. Decoding moves each letter back by the shift. With a shift of 3, HELLO becomes KHOOR, and KHOOR decodes to HELLO. The two alphabet rows under the shift box show exactly which letter replaces which.
Brute force: when you do not know the shift
A Caesar cipher has only 25 usable shifts, so the quickest attack is to try them all. In Brute force mode the decoder decodes your text with every shift and ranks the results. Two signals decide the order. The first is letter frequency: English leans on E, T and A and rarely uses Q, X or Z, so the tool compares the letter counts of each candidate with typical English using a chi-squared statistic, where a lower number means a closer match. The second is the word hit rate, the share of letters that make up real words from a 172,000-word list. A wrong shift produces gibberish that scores low on both. The right one reads like English. The two scores are blended into the ranking, and a confidence label says how clear the winner is.
Worked example
Press Example to load the coded text “Tlla tl ha aol vsk zavul iypknl ha upul.” Brute force puts shift 7 at the top, with every letter inside a dictionary word, and decoding with 7 gives “Meet me at the old stone bridge at nine.” The other 24 candidates are gibberish with far lower word hit rates. Each row has a Use button that opens that shift in Decode mode.
Case, punctuation and ROT13
Preserve case keeps capitals where they were; turn it off for all-capital output. Preserve spaces and punctuation leaves everything except A to Z untouched; turn it off for a letters-only block, the way ciphertext is often written. The ROT13 button sets the shift to 13. Since 13 is half of 26, doing it twice gives back the original, so one button covers both directions.
Solving a Caesar cipher by hand
You can often crack a short message with a pencil. Count the letters and find the most frequent one, which is probably E. If that letter is L, which sits seven places after E, try a shift of 7. A single-letter word is likely A or I, and a three-letter word that repeats is likely THE or AND, so each of these gives you a shift to test. The decoder simply does that bookkeeping for all 25 shifts at once.
When brute force is not enough
Very short messages can fit more than one shift, and names, abbreviations or non-English text can mislead the word check, so scan the first few candidates. If none of the 25 reads as language, the message probably uses a different cipher. A general substitution cipher swaps each letter for an arbitrary one rather than a fixed shift, and the Cryptogram Solver is the natural next step.
Disclaimer: This tool is for learning, puzzles and entertainment. A Caesar cipher has only 25 usable keys and can be broken in moments, so it provides no real secrecy: do not use it to protect passwords, personal data or anything sensitive. The ranking of shifts is a statistical guess, not a proof, so verify the decoded text before relying on it.