TOOLEncode and decode with a shift cipher
The Caesar cipher shifts every letter along the alphabet by a fixed amount — one of the oldest and simplest ciphers there is. Set a shift to encode, use a negative shift (or the reverse button) to decode, or hit ROT13 for the classic shift-13 that encodes and decodes with the same action. Non-letters are left untouched.
Good to know
A Caesar cipher is fun for puzzles and hiding spoilers, but it offers no real security — it's trivial to break. For anything sensitive you need proper encryption. Learn how modern encoding differs in what is Base64 encoding, or try the Base64 tool.
A worked example
With a shift of 3, each letter moves three places along the alphabet: HELLO becomes KHOOR (H→K, E→H, L→O, L→O, O→R). To decode, apply a shift of −3 (or the reverse button) and KHOOR returns to HELLO. ROT13 is the same idea with a shift of 13 — and because the alphabet has 26 letters, applying it twice brings you back to the start, so one button both encodes and decodes.
How to use the cipher
- Type or paste your text.
- Set a shift from 1 to 25 to encode, or use a negative shift to decode.
- Or click ROT13 for the classic shift-13 preset, then copy the result.
A Caesar cipher is fun for puzzles, hiding spoilers or learning how encoding works, but it offers no real security. For genuine encoding of data, see the Base64 tool and what is Base64 encoding.
Frequently asked questions
What is a Caesar cipher?
A Caesar cipher shifts every letter forward in the alphabet by a fixed amount. Shift by 3 and A becomes D, B becomes E, and so on, wrapping around from Z back to A.
What is ROT13?
ROT13 is a Caesar cipher with a shift of 13. Because the alphabet has 26 letters, applying ROT13 twice returns the original text, so the same action encodes and decodes.
Is a Caesar cipher secure?
No. It is a simple, easily broken cipher meant for puzzles, obscuring spoilers, or learning about cryptography — not for protecting sensitive information.