Caesar Cipher Encoder and Decoder
A Caesar cipher encodes text by shifting every letter a fixed number of places along the alphabet. Type your text below, choose encode or decode, and set the shift (or press ROT13). The result updates instantly, and it all runs in your browser.
What is a Caesar cipher?
A Caesar cipher is one of the oldest and simplest ways to encode a message. You pick a number, the shift, and move every letter that many places along the alphabet. With a shift of 3, A becomes D, B becomes E, and so on, wrapping around so X becomes A. To read the message back, you shift the same amount in the other direction. It is named after Julius Caesar, who is said to have used a shift of 3 for his private correspondence.
This tool does the shifting for you. Type your text, choose encode or decode, and set the shift with the slider. The result updates as you type, and letters keep their case while numbers, spaces and punctuation pass through unchanged. The ROT13 button is a shortcut for a shift of 13, the most common variant, where applying it twice returns the original text.
How to crack a Caesar cipher
Because there are only 25 possible shifts, a Caesar cipher is easy to break even without the key. You simply try every shift until the text reads normally. To make that quick, this page can show you all 25 shifts of your input at once, so you can scan down the list and spot the one that turns gibberish into words.
That is also the reason a Caesar cipher is not real security. It is a fun puzzle and a great way to learn the idea of encryption, but anyone can brute-force it in seconds. For genuinely protecting information you need modern cryptography, not a letter shift.
Where people use it
Caesar ciphers turn up in puzzle books, escape rooms, treasure hunts, classroom lessons on cryptography, programming exercises, and games where a light, solvable code adds fun. ROT13 in particular is a long-standing internet convention for hiding spoilers or punchlines, since a quick toggle reveals the text.
Everything happens in your browser. Nothing you type is uploaded or stored on a server, and your most recent text is kept only in your own browser so it survives a refresh.
Frequently asked questions
How do I decode a Caesar cipher without the shift?
Switch to the all-shifts view (or set Decode and try each shift). With only 25 possibilities you can scan every shift of your text and pick the one that reads as real words. This tool can list all 25 at once to make it fast.
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 button both encodes and decodes. It is often used online to hide spoilers.
Does it change numbers and punctuation?
No. Only letters are shifted. Numbers, spaces and punctuation pass through unchanged, and letters keep their upper or lower case.
Is a Caesar cipher secure?
No. It is trivially easy to break by trying all 25 shifts, so treat it as a puzzle or a learning tool, not real protection. Use modern encryption for anything sensitive.
Is my text private?
Yes. The tool runs entirely in your browser. Nothing you type is uploaded or stored on a server.
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