Free Caesar Cipher Tool
The Caesar Cipher tool encrypts or decrypts text by shifting each letter a set number of places in the alphabet. Choose a shift value and the direction, then process your text.
Try the ROT13 tool for the shift of 13, or move up to the keyed Vigenère Cipher once a fixed shift stops being interesting.
How to use the Caesar Cipher
- 1 Enter the text you want to encode or decode.
- 2 Choose the shift amount, or leave it at the classic three.
- 3 Choose encrypt or decrypt.
- 4 Copy the output, and try other shifts to see how the text changes.
How to Use
Enter your text, pick a shift (1–25), and choose Encrypt or Decrypt. Only letters shift; digits, spaces, and punctuation are unchanged.
- Adjustable shift (1–25)
- Encrypt and decrypt modes
- Preserves case and non-letters
Frequently asked questions
Why is the default shift three?
According to Suetonius, Julius Caesar used a shift of three for his private correspondence. There is nothing special about the number — it is simply the historical default that gave the cipher its name.
How hard is it to break?
Trivially. There are only 25 useful shifts, so an attacker can try every one by hand in a minute. Even without trying them all, letter frequency gives it away: in English, E is the most common letter, so the most common ciphertext letter is almost certainly an E.
Is ROT13 a Caesar cipher?
Yes — it is a Caesar cipher with a shift of 13. The shift was chosen because 13 is exactly half of 26, which makes the cipher its own inverse: applying it twice returns the original text.
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