ROT13 Encoder/Decoder

Type or paste text and read the ROT13-transformed version in the output box. ROT13 is its own inverse — encoding twice returns the original — so the same field handles both directions.

ROT13 isn't encryption. It's a 50-year-old Usenet convention for hiding spoilers and punchlines from casual readers. If you actually want secrecy, use AES; ROT13 is for plausible deniability and obscured-but-recoverable text.

Non-letter characters pass through untouched: digits, punctuation, whitespace, and Unicode glyphs. Only ASCII A–Z and a–z are rotated, which is the original specification.

ROT13 is a Caesar cipher with shift 13. Each ASCII letter is replaced with the letter 13 positions later in the alphabet, wrapping around: A↔N, B↔O, ..., M↔Z. Because the English alphabet has 26 letters, applying ROT13 twice returns the original text. The same code works as both encoder and decoder. Non-letter characters (digits, punctuation, whitespace, Unicode glyphs) pass through unchanged.

Worked example. Input: "Hello, World!" Output: "Uryyb, Jbeyq!" Encode again: "Hello, World!" — back to original. Mixed case is preserved: uppercase rotates within A-Z, lowercase within a-z. Numbers and punctuation untouched. The simplicity is the appeal: anyone with a 5-second tool can decode it, which is exactly the point. ROT13 is a legibility filter, not a security mechanism.

Use cases where ROT13 still earns its keep. Hiding spoilers in forum posts ("the killer is gur ohgyre"). Obscuring punchlines in puzzles. Making text un-grep-able in casual scans without protecting it from any motivated reader. Lightweight obfuscation in client-side code where the goal is to deter copy-paste, not prevent reverse-engineering. None of these are security applications — for security, use AES, ChaCha20, or any modern symmetric cipher with a real key.

The historical context. ROT13 traces to early Usenet and bulletin-board systems where users needed a casual way to mark text that shouldn't be read accidentally. The Unix `tr` command does it in one line: `tr 'A-Za-z' 'N-ZA-Mn-za-m'`. Email signatures sometimes contained ROT13'd jokes. The convention faded as the web grew, but the term and the technique persist as a kind of internet folklore.

Variants and adjacent ciphers. ROT47 extends the rotation across the full printable ASCII range (33-126), which encodes punctuation and digits too — useful when ROT13's letter-only behavior leaves too much identifiable structure. Caesar ciphers with other shifts (ROT5 for digits, ROT3 in classical examples) work the same way. Monoalphabetic substitution generally is trivially broken by frequency analysis on any non-trivial text — the technique was already obsolete before computers, let alone modern cryptography. Don't conflate playfulness with security.