Encrypt and decrypt text with the Caesar shift cipher for any shift from 1 to 25, preserving case and punctuation, plus a brute-force view of all 25 shifts.
Runs entirely in your browser — your data never leaves your device.
How to use Caesar Cipher Encoder / Decoder
What it does & when you need it
The Caesar cipher shifts every letter a fixed number of places along the alphabet —
the classic example uses a shift of three, so A becomes D. It is one of the oldest
ciphers on record and a staple of puzzles, escape rooms, homework, and capture-the-flag
challenges. This tool encrypts and decrypts with any shift from 1 to 25, and when you
do not know the key it can show all 25 possibilities at once so you can pick out the
readable line. Everything happens in your browser, so nothing you enter is uploaded.
How to use
Type or paste text into the input buffer.
Set the Shift with the slider or number box. A shift of 3 is the traditional
Caesar cipher; ROT13 is a shift of 13.
To decrypt with a known key, enter the negative shift — encrypting with 5 and
decrypting with -5 returns the original.
If the key is unknown, tick Show all 25 shifts and scan for the line that
reads as plain language. Press Ctrl/Cmd + Enter to copy the output.
Things worth knowing
Case and symbols are preserved. Only A–Z and a–z rotate, and each keeps its
case. Digits, spaces, punctuation, emoji, and accented letters pass through
untouched, so the shape of the message stays intact.
It is not real security. With just 25 keys, a Caesar cipher falls in seconds to
brute force, and letter-frequency analysis breaks longer messages even faster. Use
it for fun and light obfuscation, never for secrets. When you need genuine
protection, reach for a keyed HMAC generator.
Related ciphers.ROT13 is simply this cipher fixed at a shift of
13, which makes it its own inverse. For a different flavour of encoding, try
text to binary or the NATO phonetic alphabet.
Examples
Classic shift of three
The quick brown fox
With the default shift of 3 this becomes Wkh txlfn eurzq ira.
Wrapping past Z
XYZ and abc
A shift of 3 wraps XYZ round to ABC while abc becomes def — case is preserved.
Break it by brute force
Khoor, Zruog!
Turn on Show all 25 shifts; the shift-23 line reveals Hello, World!.
Frequently asked questions
What is a Caesar cipher?+
It is one of the oldest known ciphers, named after Julius Caesar, who used it for his correspondence. Each letter is shifted a fixed number of places along the alphabet — with a shift of 3, A becomes D and B becomes E — wrapping around from Z back to A. Only the 26 letters move; digits, spaces, and punctuation are left exactly as they are.
How do I decrypt a message?+
If you know the shift, decrypt by shifting back by the same amount: this tool accepts a negative shift, so encrypting with 5 and decrypting with -5 returns the original. If you do not know the shift, turn on "Show all 25 shifts" to brute-force it — with only 25 possible keys, the readable line is easy to spot by eye.
How is it related to ROT13?+
ROT13 is simply a Caesar cipher with a fixed shift of 13. Because 13 is exactly half of 26, applying it twice returns the original text, which makes ROT13 its own inverse. A general Caesar cipher can use any shift from 1 to 25, so it is not self-inverse unless the shift happens to be 13.
Is the Caesar cipher secure?+
Not at all. With only 25 usable keys it takes seconds to break by trying every shift, and letter-frequency analysis cracks it even faster on longer text. Treat it as a puzzle, a teaching example, or light obfuscation for spoilers — never for protecting anything sensitive. For real protection use a keyed HMAC or a modern cipher.
Does it change numbers and symbols?+
No. Only A to Z and a to z are rotated, and each keeps its case. Digits, punctuation, whitespace, emoji, and accented or non-Latin letters all pass through untouched, so the structure of the text stays intact while the letters are scrambled.