What is ROT13 Encoder?

Encode and decode text using the ROT13 Caesar cipher, which shifts each letter 13 positions in the alphabet. Since there are 26 letters, applying ROT13 twice returns the original text — it's its own inverse.

By default each Latin letter slides 13 places forward: A becomes N, B becomes O, all the way through to Z becoming M. Digits, punctuation, spaces, and accented characters pass through untouched. Because the alphabet is exactly 26 letters, encoding twice returns the original, so the same field handles both encoding and decoding without a mode switch. Switch the variant chip to ROT5 to rotate digits only, ROT18 to rotate letters and digits together, ROT47 to scramble every printable ASCII character, or Custom shift to pick any Caesar shift from 1 to 25.

How to use

1. Type or paste your text into the input field — encoding happens in real time.
2. The output appears instantly. Use the variant chips above the input to switch between ROT13, ROT5, ROT18, ROT47, or a custom Caesar shift, and the Swap button to push the output back into the input for the next round.
3. Copy the result to clipboard or download as a text file.

When to use

• Hiding spoilers, punchlines, or puzzle answers in forum posts and emails.
• Teaching the idea of a shift cipher before moving on to Caesar variations.
• Lightly obfuscating fixture data or seed strings in source code comments.

Result

Encoding 'Hello World' produces 'Uryyb Jbeyq'. Pasting 'Uryyb Jbeyq' back produces 'Hello World'. Numbers and punctuation remain unchanged.

FAQ

Is ROT13 actually secure for protecting information?

No. ROT13 is a one-step substitution with a fixed key, broken instantly by any frequency analyser or even a casual reader. Treat it as a way to keep someone from accidentally reading a spoiler, never as protection against an attacker.

Why don't numbers or symbols change?

Plain ROT13 only rotates the 26 letters. Digits, punctuation, and spaces sit outside that rotation, so they pass through untouched. If you want digits scrambled too, switch to ROT5 (digits only), ROT18 (letters and digits together), or ROT47 (every printable ASCII character) using the variant chips above the input.

Does it handle uppercase and lowercase the same way?

Yes — case is preserved. "Hello" encodes to "Uryyb", not "URYYB" or "uryyb". The cipher works on each letter independently and keeps its original case, so encoded text retains the same capitalisation pattern as the input.

What about accented letters like é or ñ?

Anything outside the basic A-Z range passes through unchanged. The cipher doesn't know how to rotate é, ä, ñ, or characters in non-Latin scripts. If the text mixes English with accents, only the unaccented letters shift; the rest stays as is.

How is ROT13 different from a Caesar cipher?

ROT13 is a Caesar cipher with the specific shift value of 13. What makes 13 special is that it's exactly half of 26, so applying it twice returns the original. Pick Custom shift in the variant chips to encode with any other value from 1 to 25, which gives you the full Caesar family — just remember non-13 shifts need the matching opposite shift to decode.

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