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ROT13 Caesar Cipher

Apply the classic ROT13 cipher: each Latin letter is shifted by 13 positions, wrapping around the alphabet. Because 13 is half of 26, applying ROT13 twice gives you back the original text. Common online for hiding spoilers or punchlines.

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How it works

Each letter A to Z and a to z is replaced by the letter 13 positions later, wrapping at the end of the alphabet. Non-letters (digits, punctuation, spaces) pass through unchanged.

How to use it

  1. Paste the text

    Drop in a spoiler, a punchline, a class-demo string, or any text you want to ROT13. Punctuation passes through unchanged.

  2. Apply the rotation

    Each Latin letter is shifted by 13 positions, wrapping at the alphabet. Non-letters (digits, spaces, punctuation) stay as is.

  3. Run twice to decode

    ROT13 is its own inverse: applying it a second time gives back the original text. No keys, no flags, no surprises.

  4. Copy the rotated text

    Take the output into a forum post that hides spoilers, a Caesar-cipher class demo, or a puzzle hint waiting to be decoded.

Use cases

Hide a spoiler in a forum post.

Quickly obfuscate a punchline.

Teach the Caesar cipher in a class.

Generate ROT13 hints for a puzzle.

When NOT to use it

  • As any kind of security. ROT13 is a public puzzle convention. Anyone can decode it instantly without a key.
  • On non-Latin alphabets. ROT13 only shifts a-z and A-Z. Cyrillic, Arabic, CJK and other scripts pass through unchanged.
  • When the goal is obfuscation that survives copy-paste. Most modern messaging apps and browsers will render the ROT13 directly without humans noticing.

Your data never leaves your browser

Every utility runs entirely on your device. Nothing is uploaded, nothing is stored on a server. You can disconnect from the internet and they keep working.

Frequently asked questions

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