Caesar Cipher Encoder & Decoder
Encode and decode Caesar shift ciphers live, with ROT13, A1Z26, Atbash, and a brute-force table of all 25 shifts. Free, instant, 100% client-side.
Cipher Tool
Shift letters by a fixed amount
Result · Caesar shift 13 encode
Brute Force — All 25 Shifts (Decoded)
Every possible Caesar decoding of your input. Scan for the readable line to crack an unknown shift.
| Shift | Text |
|---|---|
| 1 | zsszbj zs czvm |
| 2 | yrryai yr byul |
| 3 | xqqxzh xq axtk |
| 4 | wppwyg wp zwsj |
| 5 | voovxf vo yvri |
| 6 | unnuwe un xuqh |
| 7 | tmmtvd tm wtpg |
| 8 | sllsuc sl vsof |
| 9 | rkkrtb rk urne |
| 10 | qjjqsa qj tqmd |
| 11 | piiprz pi splc |
| 12 | ohhoqy oh rokb |
| 13 | nggnpx ng qnja |
| 14 | mffmow mf pmiz |
| 15 | leelnv le olhy |
| 16 | kddkmu kd nkgx |
| 17 | jccjlt jc mjfw |
| 18 | ibbiks ib liev |
| 19 | haahjr ha khdu |
| 20 | gzzgiq gz jgct |
| 21 | fyyfhp fy ifbs |
| 22 | exxego ex hear |
| 23 | dwwdfn dw gdzq |
| 24 | cvvcem cv fcyp |
| 25 | buubdl bu ebxo |
A Brief History of the Caesar Cipher
The Caesar cipher is named after Julius Caesar, who — according to his biographer Suetonius — used a shift of 3 to protect military correspondence in the first century BC. Replacing each A with a D, each B with an E, and so on was enough to confound most readers of the era, when literacy itself was rare and cryptanalysis had not yet been invented.
For nearly a thousand years it remained the best-known cipher in the Western world. The ninth-century Arab polymath Al-Kindi changed that with frequency analysis: because E, T, and A dominate English (and other languages), letter-count statistics reveal the shift almost immediately. By the Renaissance the Caesar cipher was a training exercise rather than real security.
Its legacy lives on. ROT13 — a Caesar shift of 13 — became the internet's favorite "encryption" for hiding spoilers and punchlines on Usenet, precisely because applying it twice restores the original text. Today the cipher survives in puzzle books, geocaching clues, escape rooms, and classrooms as the first stop on the road to understanding modern cryptography.
Quick Answer
The Caesar cipher is one of the oldest encryption techniques: every letter in your message is shifted a fixed number of places through the alphabet. Julius Caesar reportedly used a shift of 3, and a shift of 13 is the famous ROT13. Our free tool encodes and decodes live as you type, preserves capitalization and punctuation, supports A1Z26 (letters as numbers) and Atbash (reversed alphabet) modes, and can brute-force all 25 shifts at once — perfect for cracking unknown messages or learning classical cryptography.
How It Works
Type or paste your message — the transformation updates live as you type
Choose encode or decode, then slide the shift from 0 to 25 (13 = ROT13)
Switch to the A1Z26 or Atbash tab for those cipher modes
Copy the result, or scan the brute-force table of all 25 shifts to crack unknown text
Key Facts
- Live encode/decode with a shift slider from 0 to 25 (default 13 = ROT13)
- Preserves capitalization, spaces, digits, and punctuation
- A1Z26 mode converts letters to their 1–26 alphabet position
- Atbash mode reverses the alphabet (A↔Z, B↔Y)
- Brute-force table shows all 25 possible shifts for instant cracking
- Example: "attack at dawn" shifted by 3 becomes "dwwdfn dw gdzq"
- Self-inverse: decoding is encoding with the negative shift
- 100% client-side — your messages never leave the browser
Frequently Asked Questions
How does the Caesar cipher work?
Each letter is replaced by the letter a fixed number of positions later in the alphabet, wrapping around from Z back to A. With a shift of 3, A becomes D, B becomes E, and so on. To decode, shift each letter back by the same amount. Non-letter characters like spaces and punctuation stay unchanged.
What is ROT13?
ROT13 is the Caesar cipher with a shift of exactly 13. Because the alphabet has 26 letters, applying ROT13 twice returns the original text — encoding and decoding are the same operation. It was popular on early internet forums to hide spoilers and punchlines.
How do I decode a Caesar cipher if I do not know the shift?
Use the brute-force table. It applies every shift from 1 to 25 at once, so you can scan the 25 candidate readings and spot the one that makes sense. Only 25 possibilities exist, which is why the Caesar cipher offers no real security.
What is the A1Z26 cipher?
A1Z26 replaces each letter with its position in the alphabet: A=1, B=2, … Z=26. It is a common puzzle cipher in geocaches and escape rooms. Letters of a word are joined with dashes so encoded text like "20-8-5" reads back as "THE".
What is the Atbash cipher?
Atbash is a substitution cipher that reverses the alphabet: A becomes Z, B becomes Y, C becomes X. Like ROT13 it is self-inverse, so the same operation encodes and decodes. It originally appeared with the Hebrew alphabet.
Is the Caesar cipher secure?
No. With only 25 possible shifts it can be broken by hand in seconds, and frequency analysis breaks it even faster. It is great for learning cryptography and light puzzle fun, never for protecting real information.