Encode or decode text with ROT13 (shift 13) or any custom Caesar cipher shift 1–25. Type in either box — results update live.
This is a free, real-time encoder and decoder for ROT13 and the classic Caesar cipher. Type into either box and the other side updates instantly — there is no separate encode or decode button because a letter-shift cipher is symmetric: encoding is just shifting forward, and decoding is shifting back by the same amount.
ROT13 rotates every letter by 13 places, so "A" becomes "N" and "N" becomes "A". Because the alphabet has 26 letters and 13 is exactly half, applying ROT13 a second time returns the original text — it is its own inverse. The Caesar mode lets you pick any shift from 1 to 25, which is the more general scheme Julius Caesar is said to have used with a shift of 3. People use it to:
Everything runs local and in-browser using plain JavaScript. Your text is never uploaded, logged, or sent to a server, so you can encode and decode sensitive or private notes safely on any device.
ROT13 is a letter-substitution cipher that rotates every letter of the alphabet by 13 positions, so A becomes N, B becomes O, and so on. Numbers, spaces, and punctuation are left untouched. It is widely used online to hide spoilers and puzzle answers in plain sight.
Because the alphabet has 26 letters and 13 is exactly half of 26. Shifting forward by 13 and then by another 13 adds up to 26, which wraps all the way around back to the starting letter. So applying ROT13 to text that is already ROT13-encoded returns the original — one function both encodes and decodes.
The Caesar cipher shifts each letter forward by a fixed number of positions in the alphabet, wrapping from Z back to A. Julius Caesar reportedly used a shift of 3, turning A into D. ROT13 is simply a Caesar cipher with a shift of 13. This tool lets you choose any shift from 1 to 25 in Caesar mode.
No. ROT13 and Caesar are not real encryption and provide no security. They use no secret key, and a Caesar cipher has only 25 possible shifts, so anyone can break it by trying them all in seconds. Use them for obfuscation, fun, or learning — never to protect passwords or confidential data. For that use proper encryption or hashing.
Try every shift from 1 to 25 until readable text appears — this is called brute force, and with only 25 options it is quick. In Caesar mode, paste the encoded text into the right-hand box and drag the slider through each value, watching the decoded plain text on the left until the message makes sense.
No — only the 26 letters A–Z (in both upper and lower case) are shifted, and letter case is preserved. Digits, punctuation, spaces, emoji, and any other characters pass through completely unchanged.
It is popular for hiding spoilers, jokes, and puzzle answers in online discussions so they aren't read accidentally. It also appears in crosswords, escape rooms, capture-the-flag challenges, and classroom lessons on how substitution ciphers work and why such small keyspaces are insecure.