Text & language
Caesar Cipher
The oldest secret code of all: shift the alphabet, encode, decode — live.
Julius Caesar shifted every letter of his messages three places down the alphabet to fool his enemies; two thousand years on, his cipher is still the best doorway into cryptography. Type your text, pick a shift from 1 to 25 with the slider or the field, and the encoded message appears live — the same setting decodes, you just flip the direction. One button applies ROT13, the half-alphabet shift beloved of forums for hiding spoilers and puzzle hints. Case is preserved, and accented letters and punctuation pass through untouched. Perfect for a treasure hunt, an escape room, a classroom or a challenge between colleagues. Free and instant.
How does it work?
- Type or paste your message.
- Set the shift from 1 to 25 — or click ROT13.
- Choose encode or decode: the result updates live.
- Copy the coded message with one click.
Frequently asked questions
How does the Caesar cipher work?
Each letter is replaced by the one N places further along the alphabet, wrapping around after Z. With a shift of 3, A becomes D, B becomes E — and “ORQEO” becomes “RUTHR”. To decode, you apply the reverse shift. It is a monoalphabetic substitution cipher: simple, elegant, historic.
What is ROT13 and why is it special?
ROT13 is the Caesar cipher with a shift of 13 — exactly half the alphabet. Its party trick: the same operation both encodes and decodes, since 13 + 13 = 26. That is why forums have used it since the 1980s to veil spoilers and puzzle solutions: one click to hide, the same click to reveal.
Is the Caesar cipher secure?
Not remotely — and that is its educational value: there are only 25 possible shifts, which an attacker tries in seconds, and frequency analysis (E dominates English text) betrays it instantly. To protect real data, use modern algorithms like AES — never a historical cipher.
How do you crack a Caesar message without the shift?
Two ways: try all 25 shifts until readable text appears — with this tool, just drag the slider — or spot the most frequent letter in the ciphertext and bet it maps to E. It is the classic first exercise in cryptanalysis, and a fun one to try with kids.