Caesar Cipher

Encode and decode text with the classic Caesar shift cipher. Choose any shift from 1 to 25, switch between encode and decode, and convert messages instantly in your browser. Letters keep their case and everything else is preserved.

Whether you call it caesar cipher or shift cipher, this free tool handles it instantly in your browser.

Enter text

13 chars2 words

Options

Mode

Shift amount (1-25)

Cipher outputLive preview

Khoor, Zruog!

Ctrl+Enter to copy | Ctrl+Z to undo

Example usage

Example input

Hello, World!

Example output

Khoor, Zruog!

Batch Processing

Enter multiple inputs, one per line. Each line will be processed separately.

Input (one per line)

Results

Why this tool?

Everything runs right in your browser — no uploads, no sign-up, no waiting. Your text never leaves your device.

Quick tips

•Outputs update live as you type.
•Use the sticky copy button to grab results quickly.
•Bookmark this page for fast access.

How it works

Type or paste the text you want to encode or decode.
Set the shift amount — every letter moves that many positions through the alphabet.
Switch to decode and use the same shift to recover the original message.

Use cases

Solve and create Caesar cipher puzzles and escape-room clues.

Teach the basics of substitution ciphers in classrooms.

Decode shifted messages shared in games and CTF challenges.

Experiment with how shift values change the output.

Two thousand years of the shift cipher

The Caesar cipher is named for Julius Caesar, who — according to the Roman historian Suetonius — protected military correspondence by shifting each letter three places. It stayed genuinely useful for centuries when literacy itself was the main barrier. Its descendant ROT13 (shift 13) became the internet’s standard spoiler-hider in the Usenet era precisely because the 26-letter alphabet makes a 13-shift self-inverse.

Cryptographically, it fell to frequency analysis over a millennium ago: with only 25 possible shifts, an attacker simply tries them all. That weakness is what makes it perfect for education — it teaches the concepts of keys, encryption, and brute force in one afternoon.

Cracking a Caesar cipher by hand

Given ciphertext without a key, look for the fingerprints of English: the most frequent letter is probably E (or T); a one-letter word is A or I; a three-letter word repeating is likely THE. Take "WKH TXLFN EURZQ IRA": WKH appears where THE would be, and W→T is a shift of 3 — decode with shift 3 and the phrase resolves. With this tool you can simply try shifts 1 through 25 in seconds, but knowing the manual method is what puzzle hunts actually test.

Encoding

Explore all encoding and decoding tools

Browse every tool for this kind of task, along with helpful guides that show you how to get the most out of them.

Browse Encoding

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Supporting guides

Numbers to Letters Calculator Explained

Learn how A1Z26 decoding works, which separators to use, and how to turn number strings into readable words quickly.

Text to Hex: Fast UTF-8 Examples for Developers

Understand how text maps to bytes and hex values with clear UTF-8 examples you can copy and test.

Conversion History

FAQ

What is a Caesar cipher?

A Caesar cipher shifts every letter a fixed number of places through the alphabet. A shift of 3 turns A into D, B into E, and so on, wrapping around from Z back to A.

How do I decode a Caesar cipher?

Switch the mode to decode and enter the same shift that was used to encode it. The tool reverses the shift and returns the original text.

What if I do not know the shift?

Try each shift from 1 to 25 — there are only 25 possibilities, so you can quickly scan for the one that produces readable text.