Caesar Cipher and ROT13 — Encode, Decode and Crack

Encrypt or decrypt text with a Caesar shift or ROT13, and crack an unknown shift by trying all 25. Free, no sign-up, and your files never leave your device.

Free, with no sign-up and no watermark. The file is processed in your browser and never uploaded.

Encrypt or decrypt text with a Caesar shift from 1 to 25, or use ROT13 in one click. Don’t know the shift? Open Try all 25 — every possible decoding is listed, with the most English-looking one first.

Step by step

  1. Add your text: Type or paste into Input text.
  2. Choose a mode: Pick Encrypt or Decrypt under Mode.
  3. Set the shift: Move the Shift slider, or click ROT13. Tick Shift digits too to rotate 0–9 as well.
  4. Crack an unknown shift: Open Don’t know the shift? Try all 25 to see every option, best guess first.

Handy for

Classroom

Teach how simple ciphers work and why they’re weak.

Puzzles

Create and solve treasure-hunt clues.

ROT13 spoilers

Hide spoilers or puzzle answers in forums.

Escape rooms

Decode cipher clues quickly.

Good to know

  • Only the letters A–Z are shifted; punctuation, spaces and other scripts stay the same.

  • ROT13 is its own reverse: applying it twice gives back the original.

  • The “best guess” compares letter frequencies with typical English, so it needs a sentence or more to work well.

Questions

Is a Caesar cipher secure?

No. With only 25 possible shifts it can be broken in seconds — use it for fun, never to protect real secrets.

What is ROT13?

A Caesar cipher with a shift of 13, often used online to hide spoilers.

Is my text sent anywhere?

No. Everything is processed by your browser on your own device — nothing you type or upload is sent to a server, so it is safe to use with private notes, drafts and work documents.

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