CONVERTERS
Caesar Cipher Encoder & Decoder
Encode or decode text with a classic Caesar shift cipher.
CLASSIC CIPHER
Shift letters locally
Cipher conversion happens in the browser and is never uploaded.
Caesar cipher guide
Use this Caesar cipher encoder and decoder to shift letters forward or backward by a chosen amount. Enter text, choose Encode or Decode, select a shift from 1 to 25, and copy the result. ROT13 is included.
Everything runs in your browser. This is a toy cipher for puzzles, games, and teaching, never for protecting anything real.
How it works
The Caesar cipher is one of the oldest known substitution ciphers; Julius Caesar reportedly used a shift of three. Each letter is replaced by the letter N positions later in the alphabet (wrapping around). Shift 3 turns “HELLO” into “KHOOR”: H→K, E→H, L→O, L→O, O→R. Decoding applies the shift backwards — or, equivalently, forward by 26−N.
Non-letter characters (digits, spaces, punctuation) pass through unchanged, so the cipher preserves the shape of the original text.
ROT13 — the special case
Shift 13 on the 26-letter alphabet is its own inverse: encoding and decoding are the same operation, since 13+13 = 26 = a full wrap. ROT13 is widely used online to lightly obscure spoilers, riddles, and puzzle answers — not for security, just for a moment of deliberate reading.
Why it is not secure (and what replaced it)
There are only 25 possible shifts, so brute force is trivial — try each one and read the one that makes sense. That is why the cipher died as real cryptography: frequency analysis (comparing letter patterns to known language stats) cracks any simple substitution instantly.
Modern encryption (AES, TLS) works on completely different principles — huge key spaces and complex math. If you need real security, use a password manager and HTTPS, not a Caesar shift. If you want to hide text in a game or puzzle, ROT13 and friends are perfect.
Frequently asked questions
What is the Caesar cipher?
The oldest known cipher: each letter is shifted N positions in the alphabet. Julius Caesar reportedly used a shift of 3.
How do I decode a Caesar shift without the key?
Brute force: try all 25 shifts and read the one that forms sensible text. Tools that do this automatically are called “Caesar brute forcers.”
What is ROT13?
A Caesar cipher with shift 13. On a 26-letter alphabet it is its own inverse, so encoding and decoding are the same operation.
Is the Caesar cipher secure?
No — only 25 possible keys, and frequency analysis breaks it instantly. Use it for puzzles and games, never for real data.
Does the cipher affect numbers and symbols?
No — only letters are shifted. Digits, spaces, and punctuation pass through unchanged.
Privacy note: cipher conversion and copying happen in your browser. Your text is not submitted to NAB Tools.