ROT13 Encoder / Decoder
Encode or decode text using ROT13, ROT5, or ROT47 rotation ciphers. ROT13 shifts letters by 13 positions and is its own inverse.
ROT13 is its own inverse - encoding and decoding use the same operation. It was famously used on Usenet to hide spoilers and punchlines.
What Is ROT13?
ROT13 is a simple letter substitution cipher that replaces each letter with the letter 13 positions after it in the alphabet. Because the English alphabet has 26 letters, applying ROT13 twice returns the original text, making the same operation both the encoder and decoder. It is not encryption; it is a lightweight way to obscure text so it cannot be read at a glance.
ROT13 originated on Usenet in the 1980s as a way to hide spoilers, punchlines, and mildly offensive content. Readers who wanted to see the hidden text could apply ROT13 themselves. It remains a common convention in online forums, puzzle communities, and programming exercises.
ROT Cipher Variants
| Variant | Applies To | Shift | Example |
|---|---|---|---|
| ROT13 | Letters only (A-Z) | 13 positions | Hello → Uryyb |
| ROT5 | Digits only (0-9) | 5 positions | 12345 → 67890 |
| ROT18 | Letters + digits | ROT13 + ROT5 | Hi5 → Uv0 |
| ROT47 | All printable ASCII | 47 positions | Hello! → w6==@P |
Frequently Asked Questions
Is ROT13 secure?
No. ROT13 provides zero security. It is trivially reversible and offers no protection against anyone who recognises it. It is purely an obfuscation tool for hiding spoilers or making text unreadable at a casual glance, not a form of encryption.
Why does applying ROT13 twice give back the original?
The English alphabet has 26 letters. Shifting by 13 and then shifting by 13 again totals 26, which is a full rotation back to the starting position. This symmetry is what makes ROT13 convenient: the same function encodes and decodes.
Does ROT13 affect numbers and punctuation?
Standard ROT13 only affects letters (A-Z, a-z). Numbers, spaces, and punctuation pass through unchanged. If you need to obscure digits as well, use ROT5 for numbers or ROT47 for all printable ASCII characters.
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