ROT13 / Caesar Cipher

Shift letters by any amount, or ROT13 in one click.

About ROT13 / Caesar Cipher

A ROT13 and Caesar cipher tool that shifts every letter of your text by a fixed amount, encoding or decoding it as you type in your browser.

How to use

  1. Choose ROT13 for the fixed shift of 13, or Caesar to set your own shift.
  2. For Caesar, enter a whole number from -100 to 100. Positive values shift forward (A becomes D at shift 3); negative values shift backwards, which is how you decode.
  3. Type or paste text. The shifted text appears on the right as you type, with a Copy button.

What it does

  • Only the letters A–Z and a–z move; case is preserved. Digits, punctuation, spaces and accented or non-Latin characters are left exactly where they are.
  • Shifts wrap around the 26-letter alphabet, so a shift of 29 is the same as a shift of 3 and -1 is the same as 25.
  • ROT13 is its own inverse: applying it twice returns the original, so there is no separate decode mode.
  • To decode a Caesar message, use the negative of the shift that encoded it, or try shifts 1 to 25 until the output reads as words.
  • Not supported: Vigenère, Atbash, ROT47 (which also rotates digits and symbols), or any keyed cipher.
  • This is not encryption. A Caesar cipher has only 25 possible keys and can be broken by hand in seconds.

Example

Attack at dawn
→ ROT13          Nggnpx ng qnja
→ Caesar, shift 3  Dwwdfn dw gdzq

Privacy

The shift runs in the page. No request is made, and nothing is stored.

Frequently asked questions

What is the difference between ROT13 and a Caesar cipher?
ROT13 is a Caesar cipher with the shift fixed at 13. Because 13 is half of 26, the same operation both encodes and decodes. A general Caesar cipher can use any shift from 1 to 25.
How do I decode a Caesar cipher without knowing the shift?
There are only 25 possible shifts, so try each one until the text reads as words. Shift 3 is the one Julius Caesar is reported to have used, and ROT13 (shift 13) is the most common in modern use.
Is a Caesar cipher secure?
No. It can be broken by trying all 25 shifts or by frequency analysis, since E is the most common letter in English. Use it for puzzles and for hiding spoilers, never for anything confidential.