Caesar Cipher Decoder

Caesar cipher decoder online — crack ROT13 and classic shift ciphers instantly, no signup needed. Use the free Caesar Cipher Decoder below — enter your values and get instant results, right in your browser. Logic: each letter A-Z is shifted 13 positions forward, wrapping around the alphabet (A becomes N, N becomes A). Because 13 is half of 26, applying ROT13 twice returns the original text. Non-letters pass through unchanged.

How to use the Caesar Cipher Decoder

The Caesar cipher shifts every letter by a fixed number of positions — Julius Caesar himself reportedly used it for military messages. Its most famous form is ROT13, which shifts each letter 13 places and is its own inverse, so the same operation both encodes and decodes. This caesar cipher decoder online cracks ROT13 text instantly, making it perfect for puzzle hunts, spoiler tags, geocaching clues and classroom cryptography lessons.

  1. Paste the coded message into the input area.
  2. Make sure "ROT13" is selected in the Method dropdown.
  3. Click Convert to decode the message — ROT13 undoes itself.
  4. Encoding works the same way: type plain English and Convert to cipher it.
  5. Click Copy to use the result, or Clear to decode another message.

Formula

Logic: each letter A-Z is shifted 13 positions forward, wrapping around the alphabet (A becomes N, N becomes A). Because 13 is half of 26, applying ROT13 twice returns the original text. Non-letters pass through unchanged.

Worked example

Input "Uryyb Jbeyq", method ROT13, click Convert. Output: "Hello World" — each letter shifted back 13 places. Converting "Hello World" again returns "Uryyb Jbeyq", proving ROT13 is its own mirror. Non-letter characters pass through unchanged, so punctuation and numbers in your message stay exactly as they were.

Frequently asked questions

ROT13 rotates each letter 13 places through the alphabet. It is the most common Caesar cipher and is often used to hide spoilers and puzzle answers.

Not at all by modern standards — there are only 25 possible shifts, so it is broken in seconds. It is a learning and puzzle tool only.

ROT13 is symmetric: the same shift both encodes and decodes. Applying it to cipher text reveals the message.

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