Free Caesar Cipher & ROT13 Encoder/Decoder
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About the Caesar Cipher & ROT13
Encode or decode text with ROT13 or any Caesar cipher shift (1–25) — see the result live as you type, all in your browser with no upload.
How to use the Caesar Cipher & ROT13
- 1Type or paste your text into the input box.
- 2Leave the shift at 13 for ROT13, or drag the slider to any value (1–25) for a Caesar cipher.
- 3The result appears instantly — switch to Decode to turn an encoded message back, at any shift.
- 4Click Copy to copy the output to your clipboard.
Frequently asked questions
What is ROT13?
ROT13 ('rotate by 13') is a simple Caesar cipher that replaces each letter with the one 13 positions after it in the alphabet. Because the alphabet has 26 letters, applying ROT13 twice returns the original text — so encoding and decoding use the same operation.
What is a Caesar cipher?
A Caesar cipher shifts every letter in the message by a fixed number of positions. Julius Caesar reportedly used a shift of 3. Any shift from 1 to 25 produces a different cipher; shift 13 is the special ROT13 case.
Are numbers and punctuation affected?
No — only the 26 English letters (A–Z and a–z) are shifted. Digits, spaces, punctuation and other characters pass through unchanged.
Is this a secure encryption method?
No. Caesar ciphers are trivially broken and should not be used to protect sensitive information. They are useful for light obfuscation, puzzle spoilers, and learning about cryptography.