🔁 ROT13 Encoder / Decoder
ROT13 rotates each letter halfway round the alphabet, the same click both hides and reveals, because doing it twice returns the original.
Transformed in your browser, nothing you type is uploaded.
How the rot13 encoder / decoder works
ROT13 ("rotate by 13") replaces each letter with the one 13 places along the alphabet: A↔N, B↔O, and so on. Numbering the letters A = 0 to Z = 25, the output is (position + 13) mod 26, the "mod 26" wraps letters past Z back to the start, so N (13) + 13 = 26, which wraps to 0 (A). Because 13 is exactly half of 26, adding 13 twice returns you to the original, so a single operation both encodes and decodes. Uppercase and lowercase are rotated within their own ranges, and non-letters, digits, spaces and punctuation, are left untouched.
ROT13 provides no security whatsoever; its purpose is to lightly obscure text that a reader shouldn't see by accident, spoilers, puzzle answers, joke punchlines, offensive words on old forums. It's a convention for "look only if you mean to", not a cipher for secrets.
Frequently asked questions
What does ROT13 do?
It shifts every letter 13 positions along the alphabet (A becomes N, N becomes A). Since the alphabet is 26 letters, this is a half-rotation, and applying it twice returns the original text.
Why is the same button used to encode and decode?
Because ROT13 is its own inverse, rotating by 13 twice is a rotation by 26, which lands back where you started. So there is only one operation.
What is ROT13 used for?
Hiding text in plain sight where secrecy doesn't matter, spoilers, puzzle solutions, punchlines. It ensures you only read the hidden text if you deliberately decode it.
Is ROT13 secure?
No. It's a fixed, keyless substitution anyone can reverse instantly. It obscures, it doesn't protect. For real protection use encryption.
What does "HELLO" become in ROT13?
URYYB. H (7) + 13 = 20 (U), E (4) + 13 = 17 (R), L (11) + 13 = 24 (Y) twice, O (14) + 13 = 27 which wraps to 1 (B). Running URYYB through ROT13 again gives back HELLO.
Is ROT13 the same as a Caesar cipher?
Yes, ROT13 is exactly a Caesar cipher with a shift of 13. What makes 13 special is that it is half of 26, so encoding and decoding are the same operation, which is not true of other Caesar shifts.
Does ROT13 change numbers or symbols?
No. Standard ROT13 rotates only the 26 letters and leaves digits, spaces and punctuation as they are. If you need numbers and symbols scrambled too, ROT47 rotates the full range of printable ASCII.
Is my text uploaded?
No, ROT13 is applied in your browser.