ROT13 Encoder Decoder
Encode or decode text using the ROT13 substitution cipher. English letters are rotated by 13 positions while numbers, punctuation, spaces and other characters remain unchanged.
Applying ROT13 twice restores the original text
What Is ROT13?
ROT13 is a simple substitution cipher that replaces every English alphabet letter with the letter located 13 positions away. The name ROT13 means “rotate by 13.”
Because the English alphabet contains 26 letters, applying a 13-position rotation twice returns every letter to its original position. This is why the same ROT13 operation is used for both encoding and decoding.
How to Use the ROT13 Encoder Decoder
Enter the text you want to transform and click Apply ROT13. The calculator rotates alphabetic characters while preserving numbers, spaces, punctuation and capitalization.
ROT13: Uryyb Jbeyq
To decode the result, enter Uryyb Jbeyq and apply ROT13 again.
ROT13 Encoding Example
ROT13: OvanelPba
Uppercase B becomes O, lowercase i becomes v, and the remaining letters follow the same 13-position rotation.
ROT13 Decoding Example
ROT13 does not require a separate decoding algorithm.
Apply ROT13
Hello World
The same substitution reverses the original transformation.
ROT13 Letter Mapping
| Letter | ROT13 | Letter | ROT13 |
|---|---|---|---|
| A | N | N | A |
| B | O | O | B |
| C | P | P | C |
| D | Q | Q | D |
| E | R | R | E |
| F | S | S | F |
| G | T | T | G |
| H | U | U | H |
| I | V | V | I |
| J | W | W | J |
| K | X | X | K |
| L | Y | Y | L |
| M | Z | Z | M |
Why ROT13 Uses a Shift of 13
Thirteen is exactly half of the 26-letter English alphabet.
A letter shifted by 13 positions reaches the opposite half of the alphabet. Shifting the result by another 13 positions completes a full 26-position cycle.
ROT13 and Numbers
Standard ROT13 does not transform digits.
ROT13: Uryyb 2026
Only alphabetic characters change.
ROT13 and Punctuation
Spaces, commas, periods, brackets, symbols and other non-letter characters remain unchanged.
ROT13: Uryyb, Jbeyq!
Does ROT13 Preserve Letter Case?
Yes. Uppercase letters remain uppercase and lowercase letters remain lowercase after transformation.
NOP klm
ROT13 vs Caesar Cipher
ROT13 is a special Caesar cipher with the rotation fixed at 13 positions. A general Caesar cipher may use other shift values.
| Method | Shift | Decode |
|---|---|---|
| ROT13 | 13 | Apply ROT13 again |
| Caesar Cipher | Variable | Apply inverse shift |
Common ROT13 Uses
ROT13 has historically been used for hiding puzzle answers, spoilers, joke punchlines and other text that users may want to obscure without using real encryption.
It is also common in programming examples because the algorithm is small and demonstrates character processing and modular arithmetic.
ROT13 in Programming
For each alphabetic character, the letter position is shifted by 13 and wrapped around the alphabet when necessary.
Uppercase and lowercase letters are handled separately so capitalization is preserved.
Is ROT13 Secure?
No. ROT13 should not be used for passwords, sensitive information, confidential communication or security purposes.
There is no secret key. Anyone who recognizes the transformation can reverse it immediately by applying ROT13 again.
ROT13 vs Encoding
ROT13 is a letter-substitution transformation rather than a binary encoding format such as Base64, hexadecimal or ASCII representation.
It is nevertheless useful alongside encoding tools when working with text transformations and simple data-obfuscation exercises.
ROT13 Processing in Your Browser
The transformation is calculated directly in the browser using JavaScript. No external API is required to generate the result.
This keeps the tool fast and allows the transformation to happen immediately after the button is clicked.
Important ROT13 Notes
Only English alphabet letters are changed.
Uppercase letters remain uppercase.
Lowercase letters remain lowercase.
Numbers are unchanged.
Spaces and punctuation are unchanged.
ROT13 always uses a 13-position shift.
The same transformation performs both encoding and decoding.
Applying ROT13 twice returns the original text.