Guides JP

Caesar Cipher Tool

Enter text and a shift amount to encrypt or decrypt with a Caesar cipher. ROT13 and full brute-force supported.

Last updated: 2026/10/16 Text Feedback & bug reports
Input Text
Settings
Mode
Result
Brute Force All Shifts (0-25)

For decrypting ciphertext with an unknown shift. Scan all results to find the readable one.

How to Use

1

Enter Text

Type or paste the text you want to encrypt or decrypt into the input field.

2

Choose Shift & Mode

Select a shift amount (0-25) and a mode (Encrypt / Decrypt). You can also set ROT13 with one click.

3

View & Copy the Result

The result updates in real time. Use the Copy button to save it to your clipboard.

4

Crack Unknown Ciphers

If the shift is unknown, check the brute-force list and look for the readable line.

What Is a Caesar Cipher?

The Caesar cipher is one of the oldest and simplest encryption methods, replacing each letter with another a fixed number of positions down the alphabet. It is named after Julius Caesar, who reportedly used it. With a shift of 3, for example, A becomes D and B becomes E. This tool shifts only alphabetic characters and leaves numbers, symbols, and other characters unchanged.

Key Features

  • Real-time ConversionResults update instantly as you type or change the shift amount.
  • One-click ROT13Apply ROT13 (shift 13) with a single button, where encrypting and decrypting are identical.
  • Brute Force All ShiftsSee every result from shift 0 to 25 to crack ciphertext with an unknown key.
  • In-browser ProcessingAll processing runs in your browser. Your text is never sent to any server.

Use Cases

  • Learning cryptography and creating study materials
  • Designing puzzles for mystery and escape games
  • Solving classic cipher challenges in CTF competitions
  • Understanding algorithms while learning to program
  • Hiding spoilers with ROT13 on social media and forums

FAQ

What is the difference between a Caesar cipher and ROT13?
ROT13 is the special case of a Caesar cipher with a shift of 13. Because the alphabet has 26 letters, shifting by 13 makes encryption and decryption identical. The ROT13 button in this tool simply sets the shift to 13.
Are Japanese characters, numbers, and symbols converted?
No. Only the half-width Latin letters (A-Z, a-z) are shifted. Numbers, symbols, spaces, and other characters are preserved, so the structure of your text stays intact.
Can I decrypt ciphertext when I do not know the shift?
Yes. The "Brute Force All Shifts (0-25)" list shows every possible result. Find the one that reads as meaningful text to identify the shift and recover the message.
Is text encrypted with a Caesar cipher actually secure?
No. A Caesar cipher has only 26 possible keys and can be broken instantly by brute force, so it is not secure for protecting real secrets. Use it for learning, puzzles, or hiding spoilers. This explanation is general information and does not guarantee the protection of confidential data.
Is my text sent to a server?
No. This tool runs entirely in your browser using JavaScript. Your text is never sent to or stored on any external server, so you can use it with confidence.

Related Tools

Text Encrypt / Decrypt AES-encrypt/decrypt text with a passphrase, fully in-browser Morse Code Translator Translate text and Morse code with audio playback ASCII Converter Convert between text and ASCII/Unicode codes

Popular Tools

Character Counter Count characters, words, and lines in real-time JSON Formatter Format and validate JSON with syntax highlighting QR Code Generator Create custom QR codes with logo, colors & styles Password Generator Generate secure random passwords with one click Base64 Encoder Encode and decode text or files to Base64 IP Address Checker Check your global IP address

Related Guides

What Is the Caesar Cipher? How Letter Shifting, ROT13, and Cracking Work Learn what the Caesar cipher is from the ground up: how this classic cipher shifts letters by a fixed amount, how to encrypt and decrypt, the idea of ROT13 and the key (shift amount), why a brute-force attack breaks it easily, how it differs from modern encryption, and how to use it for learning and fun.