Does ROT13 need a key?

No separate secret key is used. The convention fixes a 13-letter shift on A to Z. Changing the shift or alphabet produces a different Caesar transformation.

Does ROT13 change numbers?

Standard ROT13 changes A to Z, preserving letter case. Digits, punctuation and spaces remain unchanged.

How can I convert ROT13 back to English?

Paste the ROT13 text while A to Z and shift 13 are selected. Applying ROT13 again restores the original supported letters; the operation does not translate languages.

ROT13 Decoder and Encoder

This workflow opens Caesar on A to Z with shift 13: URYYB becomes HELLO. ROT13 is its own inverse because two rotations of 13 equal one full 26-letter rotation. Paste either plain text or ROT13 text at these settings; use Copy or download the result and steps. The general controls remain available if you want to try another cipher or alphabet.

Cipher text18 characters

Plain textCaesar, shift 13

Hello, World! 2026

decode A = 0 to Z = 25, wrapping after Z; case kept; spaces, digits and punctuation pass through

plain	A	B	C	D	E	F	G	H	I	J	K	L	M
cipher	N	O	P	Q	R	S	T	U	V	W	X	Y	Z
plain	N	O	P	Q	R	S	T	U	V	W	X	Y	Z
cipher	A	B	C	D	E	F	G	H	I	J	K	L	M

U20 - 13 = 7, H
r17 - 13 = 4, e
y24 - 13 = 11, l
y24 - 13 = 11, l
b1 - 13 = -12, -12 + 26 = 14, o
J9 - 13 = -4, -4 + 26 = 22, W
b1 - 13 = -12, -12 + 26 = 14, o
e4 - 13 = -9, -9 + 26 = 17, r
y24 - 13 = 11, l
q16 - 13 = 3, d

encode shift forward 13 to encode again

Shift

Alphabet

Method: Caesar, shift 13

Letters shifted: 10

Passed through: 8

Encode: shift forward 13 to encode again

Every letter moves the same number of places along the alphabet and wraps round after the last one. Type your own alphabet to shift digits or symbols as well.

Every shift, ranked

All 25 shifts were undone. For each result the letters A to Z are counted and compared with standard English letter frequencies by a chi-squared score, and lower is closer to English. The ranking is an estimate, not a solution: read down until a line makes sense.

Shift 16rank 1, score 24.0
Ebiil, Tloia! 2026
Shift 24rank 2, score 24.8
Wtaad, Ldgas! 2026
Shift 13rank 3, score 28.4
Hello, World! 2026
Shift 9rank 4, score 60.0
Lipps, Asvph! 2026
Shift 22rank 5, score 62.1
Yvccf, Nficu! 2026

Only 10 letters to score. Under 40 letters one unusual word can reorder the list, so read every row.

Textbook checks, one per method

Each row is worked by the same code as the stage above. Load puts it in the workbench with its keys.

Caesar, shift 3ABCXYZ
DEFABC
Keyword KRYPTOSKNOWLEDGE IS POWER
DGHVETPST BM IHVTL
Polybius 5 x 5, I and J share cell 24JAM
24 11 32, which decodes as IAM
A1Z26, numbers separated by spaces1 26
AZ
Nihilist, square ZEBRAS, key RUSSIANDYNAMITE WINTER PALACE
37 106 62 36 67 47 86 26 / 104 53 62 77 27 55 / 57 66 55 36 54 27
Book cipher, a 40-word reference text3 17 52
error: word 52 is outside the 40-word reference, and nothing is guessed
One-time pad, key XMCKLHELLO
EQNVZ

Puzzles and teaching, not secrets. These are historical and puzzle ciphers. Caesar has only 25 shifts on A to Z, so the ranked list that Decode shows reads most messages without the key, and keyword, Polybius and A1Z26 text gives way to letter counting. The one-time pad mode shows the arithmetic of a key you type and nothing more: this tool does not make keys and makes no claim that a message stays secret.

Accuracy. Each method follows the convention shown beside it: Caesar shifts count from 0 at the first letter of the alphabet and wrap after the last, the 5 x 5 Polybius and Nihilist squares give I and J one cell, A1Z26 reads 1 26 as AZ, and a book number outside your reference is an error, never a guess. The ranked list of Caesar shifts is an estimate from English letter frequency. These are historical and puzzle ciphers, not modern secure encryption, and the one-time pad mode only shows the arithmetic of the key you type, with no claim that it keeps a message secret.

Common questions

Does ROT13 need a key?: No separate secret key is used. The convention fixes a 13-letter shift on A to Z. Changing the shift or alphabet produces a different Caesar transformation.
Does ROT13 change numbers?: Standard ROT13 changes A to Z, preserving letter case. Digits, punctuation and spaces remain unchanged.
How can I convert ROT13 back to English?: Paste the ROT13 text while A to Z and shift 13 are selected. Applying ROT13 again restores the original supported letters; the operation does not translate languages.

Each method follows the convention shown beside it: Caesar shifts count from 0 at the first letter of the alphabet and wrap after the last, the 5 x 5 Polybius and Nihilist squares give I and J one cell, A1Z26 reads 1 26 as AZ, and a book number outside your reference is an error, never a guess. The ranked list of Caesar shifts is an estimate from English letter frequency. These are historical and puzzle ciphers, not modern secure encryption, and the one-time pad mode only shows the arithmetic of the key you type, with no claim that it keeps a message secret.