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ROT13 / Caesar Cipher

Caesar cipher with adjustable shift.

beats rot13.com edge: Adjustable shift + live encode
input
output
shift 13
Guide

About ROT13 / Caesar Cipher

Apply ROT13 by default — the classic 13-position alphabet shift used to obscure spoilers, jokes, or simple ciphers. Or pick any shift from 1 to 25 for a general Caesar cipher. The cipher is symmetric at 13 (encode = decode), and at any shift, applying it twice with shift N and shift 26-N restores the original.

ROT13’s quiet usefulness

Real cryptography is for real secrets. ROT13 is for not-quite-secrets — text you want to obscure from casual scanning while keeping it trivially decodable. Spoilers in Reddit comments. Joke punchlines on Usenet. Easter-egg keys in puzzle games.

The cipher is so weak that “decoded” by hand is a few seconds of effort, which is the point — anyone determined gets the content; anyone scrolling sees gibberish.

How the cipher works

Each letter shifts forward by N positions in the alphabet. ROT13 = shift 13. A → N, B → O, M → Z, N → A (wrap around).

ABCDEFGHIJKLMNOPQRSTUVWXYZ
↓
NOPQRSTUVWXYZABCDEFGHIJKLM

Apply the same shift to ROT13 output and you get the original back — that is what makes 13 special. Other shifts need shift 26-N to invert.

Common workflows

Hide a spoiler. Wrap a sentence in ROT13 in a forum post. Readers who want to be spoiled can decode; others scroll past gibberish.

Easter eggs. Encode a hint in a project. ROT13 is enough to evade casual reading, easy enough that finders feel clever.

Caesar cipher puzzles. Set shift to N. Build crosswords or escape-room clues.

Educational example. First lesson in cryptanalysis. ROT13 falls to letter-frequency analysis instantly — a teaching exercise.

Don’t use for

  • Confidentiality (use AES)
  • Authentication (use HMAC)
  • Password storage (use bcrypt)
  • Anything where the contents matter

ROT13 is a reading filter, not a cipher.

Frequently asked questions

Is ROT13 secure?
No — and it was never meant to be. ROT13 obscures content from casual reading (spoilers, joke punchlines) but offers no cryptographic protection. Anyone can decode in seconds.
Why is ROT13 famous?
Usenet convention from the 1980s. Used to hide spoilers and offensive jokes. Survives because applying ROT13 twice gives you back the original — the same function encodes and decodes.
Other shift values?
Pick 1-25. Shift 1 = ROT1, shift 13 = ROT13. Each shift's decoder is shift 26-N (so ROT5 decodes with ROT21).
Are non-alphabet characters touched?
No. Only A-Z and a-z shift. Numbers, punctuation, whitespace pass through unchanged.
What about Unicode?
Unchanged. The shift only applies to ASCII letters; everything else passes through as-is.
For real encryption use what?
AES-GCM — modern symmetric encryption. ROT13 is for jokes; AES is for actual secrecy.
What is a Caesar cipher and how does it work?
A Caesar cipher shifts every letter a fixed number of positions down the alphabet — shift 3 turns A→D, B→E, and so on, wrapping Z→C. It's named after Julius Caesar, who used a shift of 3. ROT13 is just a Caesar cipher with shift 13. To decode, shift back by the same amount (or forward by 26 − shift). Set the shift above to encode or decode any Caesar cipher; a solver that tries all 25 shifts breaks an unknown one in seconds.
How do I ROT13 in Linux or Python?
Linux: echo "text" | tr 'A-Za-z' 'N-ZA-Mn-za-m' is the classic one-liner. Python: codecs.encode("text", "rot_13"), or str.translate with a shifted table for arbitrary Caesar shifts. This tool matches both — paste to verify before scripting.

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Last updated: 2026-07-04