ROT13 Cipher Tool
Encrypt and decrypt text with ROT13, the classic rotate-by-13 letter substitution, and see text statistics, entropy and letter frequency as you type.
100% client-side · Nothing you type is stored or sent
Letter frequency analysis
ROT13 is for hiding spoilers and learning, not for protecting secrets. Anyone can reverse it. Only the letters A to Z are converted; everything else passes through unchanged.
How the ROT13 Cipher Works
ROT13 (“rotate by 13 places”) is a simple letter substitution cipher that replaces each letter with the 13th letter after it in the alphabet. For example, HELLO becomes URYYB, and URYYB becomes HELLO again.
- ROT13 is its own inverse: the same operation both encrypts and decrypts
- It only affects the letters A to Z, in upper and lower case
- Digits, punctuation, spaces and symbols stay unchanged
- It is useful for basic obfuscation but gives no real cryptographic security
How to use the tool
- Enter or paste your text in the input field
- The ROT13 result appears as you type
- To decrypt, paste ROT13 text in the same field, or press Use result as input
- Press Copy result to copy the output to your clipboard
- View text statistics and letter frequency for your text
Classic ROT13
Rotate every letter by 13 places, the simplest Caesar-style cipher
Its Own Inverse
Apply it twice to get your original text back, so one step does both jobs
Live Conversion
Results update as you type, and the result can be moved back in to check a round trip
Letter Frequency
See which letters your text uses most, and why substitution ciphers are easy to break
Text Statistics
Characters, words, lines, letters converted, entropy and conversion time
Nothing Stored
Runs in your browser with no network requests and no history
Explore more free tools in our security tools collection, including our strong random password generator.
Frequently Asked Questions
1. What is ROT13 cipher?
ROT13 is a simple substitution cipher where each letter in the plaintext is replaced by a letter 13 positions further in the alphabet. It’s a special case of the Caesar cipher with a fixed shift of 13.
2. Is ROT13 secure for encryption?
No, ROT13 provides only basic obfuscation and should not be used for securing sensitive information. It can be easily decrypted by anyone who understands the algorithm.
3. Why is ROT13 its own inverse?
Because there are 26 letters in the English alphabet, applying ROT13 twice returns the original text. This property makes the same operation work for both encryption and decryption.
4. What characters does ROT13 affect?
ROT13 only affects alphabetical characters (A-Z and a-z). Numbers, punctuation, spaces, and special characters remain unchanged in the ciphertext.
5. What are common uses for ROT13?
ROT13 is commonly used to hide spoilers, puzzle solutions, or offensive content in online forums. It’s also used as a simple introduction to cryptography concepts.
6. Can ROT13 be used with non-English alphabets?
The standard ROT13 algorithm is designed for the 26-letter English alphabet. For other alphabets with different numbers of letters, the rotation would need to be adjusted accordingly.
7. Is anything stored or sent when I use this page?
Everything runs in your browser, the page’s content security policy blocks outgoing network requests, and nothing is saved: there is no history, and the only thing kept in local storage is your language choice.