Home Caesar cipher
Caesar cipher
hello shifted by 13 is uryyb. HELLO is URYYB. The shift runs from 1 to 25, and letters outside A–Z stay put.
Why this exists
A Caesar cipher treats the alphabet as a circle and turns every letter by the same count. Thirteen steps is half the circle, so it is called ROT13.
Decode turns the other way. The opposite of shift 1 is 25 steps, and the opposite of shift 13 is also 13 steps.
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01How to use it
Typing hello and 13 shows uryyb.
Switching to decode turns the same count the other way. uryyb and 13 become hello.
Copy puts that one line on the clipboard. Clearing the text hides the result.
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02What you get
hello and 13 are uryyb. HELLO and 13 are URYYB.
Hello, world! and 13 are Uryyb, jbeyq!.
a and 1 are b. z and 1 are a.
Enteredhello · 13
hello · 13 uryyb HELLO · 13 URYYB Hello, world! · 13 Uryyb, jbeyq! a · 1 b -
03Worth knowing
Shift 0, shift 26, and a decimal stop. 1.5 is not read.
The text runs up to 5,000 characters. Past that, it stops.
This shift is separate from Morse code. It does not turn letters into dots and dashes.
Closing the tab clears the text. Nothing is sent to a server.
Questions
- QWhat is hello shifted by 13?
- AIt is uryyb. A shift of 13 is ROT13.
- QWhat about HELLO?
- AIt is URYYB. Capitals stay capitals.
- QDoes the comma move?
- ANo. Hello, world! becomes Uryyb, jbeyq!.
- QDoes this keep a secret?
- ANo. Anyone who knows the same shift can reverse it, and the text is not sent to a server.
How this page works it out
This page shifts A through Z and a through z by the same count. hello shifted by 13 is uryyb. h becomes u, e becomes r, l becomes y, and o becomes b. z shifted by 1 is a, and a shifted by 25 is z. The alphabet is a circle, so the end returns to the start.
A shift of 13 is ROT13. 13 plus 13 is 26, one full turn, so uryyb shifted by 13 again is hello. Capitals stay capitals, so HELLO becomes URYYB. Hello, world! becomes Uryyb, jbeyq!, and the comma, the space, and the exclamation mark stay. café becomes pnsé, and é and Hangul do not move.
Decode shifts by 26 minus the shift. Decoding b by 1 returns a. The opposite of shift 13 is also 13. The shift runs from 1 to 25, and 0, 26, and 1.5 stop. The text runs up to 5,000 characters. This shift is separate from Morse code and does not keep a secret. The text changes only in this browser and is not sent to a server.