ROT13 (rotate by 13 places) is a simple letter substitution cipher that replaces each letter with the letter 13 positions after it in the alphabet. A becomes N, B becomes O, and so on. Since the alphabet has 26 letters, applying ROT13 twice returns the original text, making it self-inverse — the same operation encodes and decodes.

What is ROT13 used for?

ROT13 is used to obscure text so it cannot be read accidentally — spoiler alerts, puzzle answers, and offensive jokes on forums. It provides no real security (it is trivially reversible) but serves as a "please look away" signal. It was widely used on Usenet newsgroups and is still seen on Reddit and online forums.

What is the difference between ROT13, ROT5, ROT18, and ROT47?

ROT13 shifts only letters (A-Z) by 13. ROT5 shifts only digits (0-9) by 5. ROT18 combines both: ROT13 for letters and ROT5 for digits. ROT47 shifts all printable ASCII characters (! through ~, codes 33-126) by 47, encoding letters, digits, and symbols alike.

No. ROT13 is not encryption in any security sense. It is a trivial substitution cipher that offers zero security — anyone who knows what ROT13 is can decode it instantly. It is classified as an obfuscation or encoding technique, not encryption. Never use ROT13 to protect sensitive data.

What is a Caesar cipher?

A Caesar cipher shifts each letter in the plaintext by a fixed number of positions in the alphabet. ROT13 is a Caesar cipher with shift 13. ROT1 shifts by 1 (A→B), ROT3 shifts by 3 (A→D). Named after Julius Caesar, who reportedly used a shift of 3 to encrypt military messages.

How do I decode ROT13 without a tool?

Write out the alphabet twice: ABCDEFGHIJKLMNOPQRSTUVWXYZ and NOPQRSTUVWXYZABCDEFGHIJKLM. For each letter in the encoded text, find it in the second row and read the letter above it from the first row. Or simply apply ROT13 again — since it is self-inverse, encoding equals decoding.

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ROT13 Encoder & Decoder

ROT13 replaces each letter with the letter 13 positions ahead in the alphabet. A becomes N, B becomes O, Z becomes M. It is self-inverse: applying ROT13 twice returns the original text. "Hello" becomes "Uryyb". ROT5 does the same for digits (0 becomes 5). ROT47 rotates all printable ASCII. A Caesar cipher uses any shift from 1 to 25.

Encode and decode text using ROT13, ROT5, ROT18, ROT47, or custom Caesar cipher shifts. ROT13 replaces each letter with the letter 13 positions after it in the alphabet. Self-inverse: encoding and decoding are the same operation.

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Presets

Cipher Type

Input

Cipher Reference

Cipher	Shift	Description
ROT13	13	Standard letter rotation. A becomes N, B becomes O. Self-inverse (encoding = decoding)
ROT5	5	Digit rotation only. 0 becomes 5, 1 becomes 6. Self-inverse for digits
ROT18	13+5	ROT13 for letters + ROT5 for digits. Encodes both letters and numbers
ROT47	47	Rotates all printable ASCII (33-126). Encodes letters, digits, and symbols
Custom	1-25	Caesar cipher with any shift value. ROT1 = A->B, ROT25 = A->Z

How to Use

1
Select cipher type
Choose ROT13 (letters), ROT5 (digits), ROT18 (both), ROT47 (all ASCII), or Custom (any shift 1-25). ROT13 is the default.
2
Enter your text
Type or paste text to encode or decode. ROT13 is self-inverse so the same operation encodes and decodes.
3
View the result
The encoded/decoded text appears instantly. Statistics show character counts and how many characters were changed.
4
Copy the result
Click Copy to copy the transformed text. Use presets to try examples like "Secret Message" (already ROT13-encoded).

Frequently Asked Questions

What is ROT13?: ROT13 (rotate by 13 places) is a simple letter substitution cipher that replaces each letter with the letter 13 positions after it in the alphabet. A becomes N, B becomes O, and so on. Since the alphabet has 26 letters, applying ROT13 twice returns the original text, making it self-inverse — the same operation encodes and decodes.
What is ROT13 used for?: ROT13 is used to obscure text so it cannot be read accidentally — spoiler alerts, puzzle answers, and offensive jokes on forums. It provides no real security (it is trivially reversible) but serves as a "please look away" signal. It was widely used on Usenet newsgroups and is still seen on Reddit and online forums.
What is the difference between ROT13, ROT5, ROT18, and ROT47?: ROT13 shifts only letters (A-Z) by 13. ROT5 shifts only digits (0-9) by 5. ROT18 combines both: ROT13 for letters and ROT5 for digits. ROT47 shifts all printable ASCII characters (! through ~, codes 33-126) by 47, encoding letters, digits, and symbols alike.
Is ROT13 encryption?: No. ROT13 is not encryption in any security sense. It is a trivial substitution cipher that offers zero security — anyone who knows what ROT13 is can decode it instantly. It is classified as an obfuscation or encoding technique, not encryption. Never use ROT13 to protect sensitive data.
What is a Caesar cipher?: A Caesar cipher shifts each letter in the plaintext by a fixed number of positions in the alphabet. ROT13 is a Caesar cipher with shift 13. ROT1 shifts by 1 (A→B), ROT3 shifts by 3 (A→D). Named after Julius Caesar, who reportedly used a shift of 3 to encrypt military messages.
How do I decode ROT13 without a tool?: Write out the alphabet twice: ABCDEFGHIJKLMNOPQRSTUVWXYZ and NOPQRSTUVWXYZABCDEFGHIJKLM. For each letter in the encoded text, find it in the second row and read the letter above it from the first row. Or simply apply ROT13 again — since it is self-inverse, encoding equals decoding.