ROT13 and Caesar Cipher
Type a text and choose a shift (13 = classic ROT13) — the letters are shifted through the alphabet automatically.
How to use the ROT13/Caesar cipher
- Type or paste your text.
- Choose a shift — 13 gives the classic ROT13, but any number from 1 to 25 works as a general Caesar cipher.
- The result updates automatically. Run the same shift on the result again for ROT13 (shift 13 only) to get the original text back.
What are ROT13 and the Caesar cipher?
A Caesar cipher shifts each letter a fixed number of positions through the alphabet — "A" with a shift of 3 becomes "D", and the alphabet wraps around at the end. ROT13 is the special case where the shift is exactly 13, half of the 26-letter alphabet, which makes it its own inverse: running ROT13 twice returns the original text.
The Caesar cipher is one of the oldest known encryption methods, named after Julius Caesar who is said to have used it for military communication. Today it has no real security value (it's trivially broken), but it's still used to hide spoilers in forum posts or as a simple puzzle/toy cipher.
ROT13 is concealment, not security
ROT13 shifts every letter thirteen places through the alphabet, and since the alphabet has 26 letters it is its own inverse — the same operation both encodes and decodes. There is no key, and therefore nothing to keep secret. Anyone who recognises the pattern can read the text immediately.
Its historical use was not security either. On older discussion forums, ROT13 was used to hide spoilers, punchlines and answers to puzzles — text the reader should not see by accident, but should be able to choose to read. Caesar ciphers with other shifts share the same weakness: with only 25 possible keys, all of them can be tried in an instant.
Frequently asked questions
Is ROT13 secure encryption?
No, ROT13 and Caesar ciphers in general provide no real security — there are only 25 possible shifts, so it's broken instantly by trying them all. It's used only to hide text temporarily, not for actual secrecy.
How do I decode a ROT13 text?
Paste the encoded text into the field with shift 13 — since ROT13 is its own inverse, applying the same shift again gives you the original text back.
What happens to numbers and punctuation?
Only letters (a–z, A–Z) are shifted. Numbers, spaces, and punctuation are left unchanged, and letter case is preserved.