Caesar cipher
Encode or decode text with a classic Caesar letter-shift cipher.
Caesar cipher
The Caesar cipher is one of the oldest and simplest substitution ciphers, named after Julius Caesar, who used it to protect his correspondence. Each letter is moved a fixed number of positions along the alphabet, so with a shift of three, A becomes D, B becomes E, and Z wraps back around to C. Paste your text, choose a shift between 1 and 25, and the result updates instantly.
Set the mode to encode to scramble a message, or to decode to recover one when you already know the shift. Because encoding by N and decoding by N are exact opposites, the same tool covers both directions. Case is preserved, and digits, spaces, punctuation and any accented or non-Latin characters pass through untouched, so only the plain A–Z and a–z letters are moved. A shift of 13 is the special case known as ROT13, which is its own inverse.
This tool is popular for classroom exercises, escape-room puzzles, capture-the-flag challenges and homework where students learn how substitution ciphers work. It is deliberately not meant to secure real secrets: with only 25 possible shifts, a Caesar cipher is trivial to break by trying each key. For genuine confidentiality use modern encryption instead.
Everything runs entirely in your browser. Your text is never uploaded to a server, so you can experiment freely with private notes. The live tally under the output shows how many letters were shifted and the total character count, and you can copy the result or send it straight to another tool.