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Caesar Cipher / ROT13

Encode or decode text with a Caesar shift cipher — ROT13 by default, or any shift from 1 to 25.

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Encode or decode text with a Caesar shift cipher — ROT13 by default, or any shift from 1 to 25.

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Optional — sensible defaults are already set.

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About Caesar Cipher / ROT13

Encode or decode text with a Caesar cipher, which replaces each letter with the one a fixed number of places further along the alphabet. Julius Caesar is said to have used a shift of three. The default shift of 13 is ROT13, which is its own inverse: applying it twice gives back the original text.

When it helps

  • Hiding spoilers, puzzle answers or punchlines in forums, the traditional use of ROT13.
  • Teaching the basics of cryptography and why simple ciphers are easy to break.
  • Solving or making puzzles for escape rooms, geocaches and CTF challenges.
  • Decoding ROT13 text found online.

Tips

  • Not secure. There are only 25 possible shifts, so anyone can try them all in seconds. Never use it for passwords or private data.
  • To crack an unknown shift, decode with each shift from 1 to 25 until the text makes sense, or compare the most common letter with 'e'.
  • Only the English letters A to Z are shifted, and case is kept. Accented letters, spaces and punctuation stay as they are.
  • 'Also rotate digits' shifts 0-9 through the ten digits using the same shift value. Use the same setting when decoding.

Good to know

Quick answers about caesar cipher / rot13 in your browser.

A Caesar cipher with a shift of 13. Because the alphabet has 26 letters, shifting by 13 twice comes back to the start, so the same operation both encodes and decodes. It was widely used on Usenet to hide spoilers.

Try every shift from 1 to 25 with the direction set to decode. Only one will produce readable words. For longer messages, the most frequent letter usually stands for E, which tells you the shift directly.

Yes. There is no sign-up, no watermark and no limit on how many files you process.

No. Files are read and processed locally in your browser, so they never leave your device.

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Part of the Text Tools collection.