Converter

ROT13 / Caesar Cipher

Encode, decode, and crack Caesar cipher and ROT13 with brute force and frequency analysis

Shift Amount13

113 (ROT13)25

Also shift numbers (0-9)

Alphabet Mapping

Plain

Cipher

Input

Output (Shift 13)

How It Works

Caesar Cipher: Each letter is shifted by a fixed number of positions in the alphabet. A shift of 3 turns A into D, B into E, etc.
ROT13: A special case of Caesar cipher with shift 13. Since 13 is half of 26, encoding and decoding are the same operation.
ROT5: Shifts digits 0-9 by 5 positions. 0 becomes 5, 1 becomes 6, etc.
ROT47: Shifts all printable ASCII characters (33-126) by 47 positions. Covers letters, numbers, and symbols.
Brute Force: Try all 25 possible shifts to decode an unknown Caesar cipher. Look for readable English in the results.

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What is ROT13 / Caesar Cipher?

Encode and decode text using ROT13 or any Caesar cipher shift from 1 to 25.

Features a visual alphabet mapping strip, real-time encoding as you type, brute force decoder showing all 25 possible shifts to crack unknown ciphers, and letter frequency analysis with bar charts comparing against standard English frequencies. Supports ROT13, ROT5 (numbers), ROT47 (all printable ASCII), and custom shifts. Preserves case, passes through non-Latin characters, and includes file upload, conversion history, and copy/download. All processing in your browser.

How to Use ROT13 / Caesar Cipher

1Type or paste your text into the input area
2Select ROT13 or set a custom Caesar cipher shift using the slider
3The encoded/decoded text appears in real time in the output area
4Use the brute force decoder to crack unknown ciphers by viewing all 25 shifts

Frequently Asked Questions

ROT13 is a simple letter substitution cipher that replaces each letter with the letter 13 positions after it in the alphabet. Since the alphabet has 26 letters, applying ROT13 twice returns the original text - the same operation encodes and decodes.

A Caesar cipher shifts each letter by a fixed number of positions. ROT13 is a Caesar cipher with a shift of 13. Julius Caesar reportedly used a shift of 3 to encrypt military messages.

Yes. The brute force decoder shows all 25 possible shifts at once, so you can visually identify which one produces readable text. The frequency analysis also helps by comparing letter distributions against standard English.

Letters are shifted while preserving case. Numbers can optionally be shifted. All other characters (punctuation, spaces, emoji, non-Latin scripts) pass through unchanged.

Paste the ciphertext and open the brute force decoder. It lists the plaintext for all 25 possible shifts at once, so you scan down and pick the row that reads as real words. The frequency analysis chart speeds this up by hinting which shift matches English letter distribution.

No. With only 25 possible shifts it can be broken instantly by trying every key, which this tool does for you. Treat it as a puzzle or a learning exercise, not as real encryption for sensitive data.

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