ROT13 Encoder / Decoder
Encode or decode text with ROT13 — the classic Caesar cipher shift of 13.
How to use this tool
- Enter text in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your rot13 result and the full breakdown beneath it.
Encode or decode text with ROT13 — the classic Caesar cipher shift of 13.
How it works
ROT13 is a simple letter substitution cipher that replaces each Latin letter with the letter 13 positions ahead in the alphabet (wrapping around from Z back to A). Because there are 26 letters, applying ROT13 twice returns the original text — encoding and decoding are the same operation, which is why this tool works as both encoder and decoder.
Enter any text and the ROT13 version is returned immediately. Non-letter characters — digits, punctuation, spaces, emoji — are passed through unchanged. ROT13 was widely used on early internet forums to obscure spoilers or punchlines so readers could choose whether to decode them.
ROT13 provides no real security. Anyone who knows the cipher (which is public knowledge) can decode it instantly. Use it for fun, light obfuscation of spoilers, or educational purposes — never for protecting sensitive information.
Worked example
Encode a spoiler warning
- Type the spoiler text: 'Darth Vader is Luke's father.'
- The tool shifts each letter by 13 positions.
- Read the encoded output.
- Paste the encoded text back in to confirm decoding returns the original.
Qnegu Inqre vf Yhxr'f sngure.
Common mistakes to avoid
- Thinking ROT13 provides meaningful security — it is purely cosmetic obfuscation that any knowledgeable person can decode in seconds.
- Applying ROT13 to text that contains non-Latin scripts — accented or non-ASCII letters are not shifted and may produce mixed output.
- Applying it an odd number of times and expecting the original — ROT13 must be applied an even number of times to return to the starting text.
Key terms
- ROT13
- A Caesar cipher with a fixed shift of 13 positions; self-inverse because the alphabet has 26 letters.
- Caesar cipher
- A substitution cipher that shifts each letter a fixed number of positions in the alphabet.
- Self-inverse
- A function that is its own inverse — applying it twice returns the input unchanged.
Frequently asked questions
- What is ROT13?
- ROT13 is a simple letter substitution cipher that replaces each letter with the one 13 positions after it in the alphabet. Applying it twice returns the original text.