A familiar greeting
Hello, World! becomes Uryyb, Jbeyq! Capitalization and punctuation stay in place.
ROT13 uses the same operation to encode and decode. Only A–Z and a–z rotate; numbers, punctuation, accented letters, and emoji stay as entered.
The 13-letter swap
A ↔ NB ↔ OC ↔ PD ↔ QE ↔ RF ↔ SG ↔ TH ↔ UI ↔ VJ ↔ WK ↔ XL ↔ YM ↔ ZA becomes N and N becomes A. Lowercase letters follow the same pairs. Two passes return every supported input exactly.
Educational obfuscation for clues and spoilers. ROT13 is immediately reversible and provides no secure encryption. Input limit: 250,000 UTF-16 code units.
Conversions run locally in your browser. This tool does not upload input or save it to browser storage.
How to use the ROT13 Encoder & Decoder
- 01
Paste plain text or an existing ROT13 message.
- 02
Read the converted result; no separate encode and decode modes are needed.
- 03
Use the letter-pair guide to inspect a substitution such as A ↔ N.
- 04
Copy or download the output, or apply ROT13 again to verify the round trip.
Examples
A mixed string
Café 123 😀 becomes Pnsé 123 😀. Only C, a, and f are rotated; the accented letter, digits, and emoji are preserved.
Why two passes undo the change
ROT13 uses a 26-letter alphabet and a shift of 13. Two shifts add up to 26, returning each supported letter to its starting position. Uppercase and lowercase letters use parallel alphabets.
A convention for optional reading
ROT13 has been used in discussion groups to make spoilers less immediately readable. That is a reading convention, not access control. The visible pair guide makes the transformation fully transparent.
Use modern cryptography for confidentiality
There is no secret key to discover: the shift is always 13. Anyone can reverse the result instantly. Use this tool for education, games, and spoiler text, never to protect passwords, private messages, or confidential files.
What to know
- 250,000 UTF-16 code units per input.
- Only Latin ASCII letters rotate; this is educational obfuscation.
Common questions
Is ROT13 a form of secure encryption?
No. It is a fixed substitution used for lightweight obfuscation. It provides no meaningful confidentiality.
Why did an accented letter stay the same?
Only ASCII A–Z and a–z participate. Expanding rotation to other scripts would require defining different alphabets and rules; this tool preserves them exactly.
Can I choose a different shift?
Use the Caesar Cipher tool for a configurable shift and a comparison of all 26 backward rotations.