ROT13 Encoder/Decoder

The ROT13 Encoder Decoder applies the classic ROT13 cipher to any text. ROT13 rotates each letter 13 positions in the alphabet — A becomes N, B becomes O, N becomes A (since rotating 13 wraps around back). Because 13 is half of 26 (the alphabet size), applying ROT13 twice returns the original text, making it self-inverse. Encode and decode use the same operation; no separate decoder is needed.

ROT13 is not serious encryption — it is trivially reversible and was never meant to hide sensitive data. Its main use is obscuring text in casual contexts: spoilers in forum discussions (someone can choose to decode if they want to see the spoiler), Easter eggs in programs, and some Usenet customs. The tool also supports related variants: ROT5 (rotates digits 0-9 by 5), ROT18 (ROT13 plus ROT5 — letters and digits together), and ROT47 (rotates all printable ASCII 33-126 by 47, covering more than just letters). All rotations preserve non-alphabetic characters unchanged.

ROT13 is a Caesar cipher with a fixed shift of 13. For each letter: A through M rotate forward by 13 to N through Z, and N through Z rotate back (by wrapping) to A through M. Because rotating 26 positions (the full alphabet) returns to the start, and 13 is exactly half, applying ROT13 twice gives back the original text. This is the self-inverse property that lets the same function encode and decode.

Case is preserved: uppercase stays uppercase, lowercase stays lowercase. Non-alphabetic characters (digits, punctuation, spaces, non-Latin scripts) pass through unchanged.

ROT5 applies the same idea to digits. Digits 0-4 rotate forward by 5 to 5-9; digits 5-9 rotate back to 0-4. Useful in combination with ROT13 when the text contains numbers that also need obfuscation.

ROT18 combines ROT13 and ROT5 in one operation. Good for alphanumeric text where you want both letters and digits obfuscated by one pass.

ROT47 shifts all printable ASCII characters (codes 33-126, which is 94 characters total) by 47. Since 94 divided by 2 is 47, ROT47 is also self-inverse. It covers much more than letters — punctuation and symbols rotate too. The output looks noisier than ROT13 because shifted punctuation characters appear in unusual positions.

Implementation: for ROT13, check if character is in A-Z or a-z; if so, compute (code - base + 13) modulo 26 and add the base back. For ROT47, check if character is in range 33-126; compute (code - 33 + 47) modulo 94 and add 33.

Non-ASCII characters like accented letters, Cyrillic, CJK, and emoji pass through ROT13 unchanged because they are not in A-Z or a-z. For true encryption of non-Latin text, use a real cipher, not ROT13.

Performance: rotation is a simple character-level transform, O(n) in text length. Multi-megabyte text rotates in milliseconds.

Compared to serious encryption (AES, RSA), ROT13 is trivially broken and should never be used for security. For actual security, use modern cryptographic libraries; ROT13 is for casual obfuscation only.

Compared to other simple ciphers (Atbash, Vigenère), ROT13 is the simplest — just a rotation by a fixed amount. Atbash reverses the alphabet (A\u2194Z); Vigenère uses a key to shift by variable amounts. ROT13 is the most basic of the family.

Compared to Base64 encoding, ROT13 is for obfuscation while Base64 is for transport (representing binary as ASCII). They serve different purposes and both are easily reversed.