🔐 ROT13 / Caesar Cipher

Encode and decode text with rotation ciphers. Adjustable shift, ROT47, and brute force mode.

Last updated: May 18, 2026 · By Λ

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Brute Force - All 25 Rotations

Free ROT13 / Caesar Cipher Tool

Apply rotation ciphers to any text with real-time encoding and decoding. ROT13 shifts each letter by 13 positions, making it its own inverse - encoding and decoding use the same operation. ROT47 extends this concept to cover numbers and symbols by rotating across the printable ASCII range (characters 33 through 126). The Caesar Cipher mode lets you choose any shift from 1 to 25. Use the brute force section to try all 25 rotations at once, which is useful for cracking an unknown shift. Every rotation, frequency count, and brute force pass is computed by the script embedded in this page, so the text you paste is never transmitted off your device.

What is a Caesar Cipher?

The Caesar cipher is one of the oldest and simplest encryption techniques in history, named after Julius Caesar, who reportedly used it to protect his military correspondence. It works by shifting each letter in the plaintext a fixed number of positions down the alphabet. For example, with a shift of 3, the letter A becomes D, B becomes E, C becomes F, and so on. When the shift reaches the end of the alphabet, it wraps around, so X becomes A, Y becomes B, and Z becomes C. Non-alphabetic characters (numbers, spaces, punctuation) are left unchanged.

ROT13 is a specific Caesar cipher that uses a shift of 13. Since the English alphabet has 26 letters, applying ROT13 twice returns the original text, making it its own inverse. ROT13 is commonly used online to obscure spoilers, puzzle answers, and mildly sensitive content. ROT47 extends the concept to the full printable ASCII range (characters 33 through 126), rotating by 47 positions across 94 characters. This tool supports all three modes: ROT13, ROT47, and custom Caesar cipher with any shift from 1 to 25. It also includes a brute force view that displays all 25 possible rotations simultaneously, which is valuable for cryptanalysis practice and puzzle solving.

How to Use This Tool

Select your cipher mode at the top: ROT13 (fixed 13-letter shift), ROT47 (covers numbers and symbols too), or Caesar Cipher (custom shift value).
If using Caesar Cipher mode, adjust the shift slider to set your desired rotation value between 1 and 25.
Type or paste your text in the Input field. The encoded or decoded output appears in real time in the Output field below.
Scroll down to the Brute Force section to see all 25 possible rotations of your input text at once, which is helpful for decoding messages when you do not know the shift value.

Key Features

Three Cipher Modes - Choose from ROT13, ROT47, or custom Caesar cipher with adjustable shift, covering different use cases from simple letter rotation to full ASCII character rotation.
Visual Alphabet Mapping - A live alphabet map shows exactly which letter maps to which, updating in real time as you change the shift value.
Brute Force View - See all 25 possible rotations of your text displayed simultaneously, making it easy to crack an unknown cipher by visual inspection.
Letter Frequency Analysis - View input and output letter frequency distributions, which is a fundamental tool in classical cryptanalysis.
Real-Time Processing - Output updates instantly as you type, with no need to click a convert button. Swap input and output with a single click.

Frequently Asked Questions

Is a Caesar cipher secure?

No. The Caesar cipher is not secure by modern standards. With only 25 possible shifts, it can be broken in seconds by trying all possibilities (brute force). It is useful for educational purposes, lightweight text obfuscation, and puzzle games, but should never be used to protect sensitive information. Modern encryption algorithms like AES use far more complex mathematical operations.

What is the difference between ROT13 and ROT47?

ROT13 only rotates the 26 English letters (A-Z and a-z), leaving numbers, punctuation, and symbols unchanged. ROT47 rotates across all 94 printable ASCII characters (from ! to ~), so numbers and symbols are also transformed. Both are their own inverse, meaning applying the same operation twice restores the original text.

How do I decode a Caesar cipher without knowing the shift?

Use the brute force section of this tool. It shows all 25 possible shifts applied to your input text. Simply scan through the results and look for the one that produces readable text. For longer messages, you can also use letter frequency analysis: in English, the most common letters are E, T, A, O, I, N, and S. Compare the frequency chart of the encoded text to expected English letter frequencies to identify the likely shift.

Why is ROT13 used on the internet?

ROT13 is used as a lightweight way to hide text that someone might not want to read accidentally, such as spoilers, joke punchlines, or puzzle solutions. It is easy to apply and reverse, and it signals to the reader that the content is intentionally obscured. It is not meant for security but rather as a simple courtesy to avoid revealing content prematurely.