Security

Caesar Cipher

Free Caesar cipher tool. Encrypt and decrypt text with a shift cipher (Caesar cipher), supporting any shift value including ROT13, with case and punctuation preserved.

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Text

Shift

Direction

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Enter text and a shift above.

Deep dive guides

A LITTLE CONTEXT · 5 MIN READClassical Ciphers: Caesar, ROT13, Atbash — and How Vigenère Beat Them All

All 5 related guides

Classical Ciphers: Caesar, ROT13, Atbash — and How Vigenère Beat Them All — How the classical ciphers work: Caesar shifts, ROT13 and Atbash as special cases, the frequency analysis that breaks them all, and the moving Vigenère key that stalled codebreakers.
Cracking a Caesar Cipher Without the Key — Why 25 shifts are always enough to try, how the chi-squared test ranks candidates against English letter frequencies, and where the method breaks down.
Transposition vs Substitution Ciphers — Two classical ways to hide a message: substitution replaces letters, transposition moves them — with a worked columnar example.
The Vigenère Cipher Explained: How the Rolling Keyword Shift Works — How the Vigenère cipher works: a repeating keyword gives every letter its own Caesar shift, with worked encrypt and decrypt examples and the real tool.
ROT13 Explained: The Shift That Is Its Own Decode Button — Half of 26 is 13: why one fixed shift both encodes and decodes, what letters survive untouched, and where ROT13 honestly belongs.

How caesar cipher works

The Caesar cipher is one of the oldest known encryption methods, named after Julius Caesar who used a shift of 3. Each letter in the message is replaced by the letter a fixed number of positions down the alphabet. A shift of 3 turns A into D, B into E, and so on, wrapping around so Z becomes C.

To decrypt, you shift each letter back by the same amount. Because there are 26 letters, a shift of 13 (ROT13) is its own inverse — applying it twice returns the original text, which is why ROT13 is popular for hiding spoilers in plain sight. This tool supports any whole-number shift, positive or negative (a shift of 29 is reduced to 3, since 26 letters wrap), and treats decrypt as the reverse shift.

Enter your text, choose a shift, and pick encrypt or decrypt. The tool shifts only letters (both cases preserved) and leaves numbers, punctuation, and other characters untouched. The Caesar cipher is a historical toy and is trivially breakable by brute force or frequency analysis — never use it for real security.

Frequently asked questions

What is a Caesar cipher?

A substitution cipher where each letter is shifted a fixed number of places down the alphabet. With a shift of 3, A becomes D and Z becomes C. Caesar reportedly used a shift of 3, which gives the cipher its name.

What is ROT13?

A Caesar cipher with a shift of 13. Because the alphabet has 26 letters, shifting by 13 twice returns the original text, so the same operation encrypts and decrypts. It is commonly used to hide spoilers online.

How is decryption done?

By shifting each letter back by the same amount used to encrypt. This tool implements decrypt as a shift in the opposite direction, and also accepts negative shifts directly.

Is the Caesar cipher secure?

No. There are only 25 possible shifts, so an attacker can try all of them by hand or computer, and frequency analysis breaks it even without knowing the shift. Use it only for puzzles, games, and learning — never for protecting real data.

Caesar Cipher

Deep dive guides

How caesar cipher works

Frequently asked questions

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