ROT13 Encoder / Decoder

Encode or decode text using ROT13, ROT47, or a custom Caesar cipher shift. ROT13 is its own inverse — encode and decode with the same operation.

Input
Output (ROT13 / decoded)

ROT13 shifts every letter by 13 positions. Non-alphabetic characters are preserved unchanged. Since 13+13=26, encoding and decoding use the same operation.

Input
Output (ROT47 / decoded)

ROT47 rotates all printable ASCII characters (! to ~, 94 chars) by 47 positions. Unlike ROT13 it also obfuscates digits and punctuation.

Shift
13
125
Input
Output (encoded)

To decode, set the shift to 26 − N (e.g., shift 13 encodes and decodes, shift 3 decodes with shift 23).

Frequently Asked Questions

ROT13 (Rotate 13) is a substitution cipher that replaces each letter with the letter 13 positions ahead of it in the alphabet. Because the English alphabet has 26 letters, applying ROT13 twice returns the original text — it is its own inverse. It was commonly used in Usenet newsgroups to obscure spoilers and offensive jokes.
No. ROT13 provides no real cryptographic security. It offers "security through obscurity" only — anyone who knows what ROT13 is can decode it instantly. Use ROT13 only for obscuring spoilers, puzzles, and similar casual uses. For real security, use AES, RSA, or other modern cryptographic algorithms.
ROT47 extends the ROT principle to all printable ASCII characters from ! (code 33) through ~ (code 126), a set of 94 characters. It rotates by 47 positions within that range. Unlike ROT13, it also obfuscates digits, punctuation, and symbols — but it is just as easy to decode.
A Caesar cipher shifts each letter by a fixed number of positions in the alphabet. Julius Caesar reportedly used a shift of 3 — A becomes D, B becomes E, etc. ROT13 is just a Caesar cipher with a shift of 13. Caesar ciphers are trivially broken by trying all 25 possible shifts.
Applying ROT13 to ROT13-encoded text always returns the original plaintext. This is the defining property of ROT13: since 13 + 13 = 26 (the alphabet size), two applications form a full cycle. No other shift value (between 1 and 25) has this property.
Try all 25 possible shifts — this is called a brute-force attack. For longer texts, use frequency analysis: in English, the most common letter is E (~13%), followed by T, A, O, I, N. Match the most frequent ciphertext letter to E to guess the shift.
ROT13 uses a fixed shift of 13 for every letter. A Vigenère cipher uses a repeating keyword to produce a variable shift per letter — making it harder to break by frequency analysis, though still breakable. ROT13 is trivially reversible; Vigenère was once called "le chiffre indéchiffrable."
Never use ROT13 (or any simple cipher) for passwords. ROT13 provides zero security. Passwords must be stored using a cryptographic hash function with a unique salt, such as bcrypt, scrypt, or Argon2.
Yes. Common variants include: ROT5 (rotates digits 0-9 by 5); ROT18 (ROT13 for letters + ROT5 for digits, combined); ROT47 (rotates all printable ASCII); and ROT-N for any custom shift 1-25.
Because it is the only Caesar shift where encoding and decoding are the same operation. This made it convenient for Usenet: readers could decode with the same tool used to encode, without remembering a key.

About This ROT13 Encoder / Decoder

This free ROT13 encoder converts any text to ROT13, ROT47, or a custom Caesar cipher rotation. ROT13 is self-inverse — the same operation decodes what it encodes. All processing happens in your browser.

When to use this tool

  • Hiding spoilers in forum posts or emails
  • Solving puzzle challenges that use ROT13 or Caesar cipher
  • Teaching substitution ciphers and classical cryptography
  • Quickly obfuscating text for non-security purposes

Standards & References

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Related Articles

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Text Jun 21, 2026
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Why ROT13's Encode Button and Decode Button Do the Same Thing — and Why That's the Point
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