Tool to encode and decode messages with ROT-18 cipher, simple and fast method to encrypt letters and numbers online.
ROT-18 Cipher - dCode
Tag(s) : Substitution Cipher
dCode is free and its tools are a valuable help in games, maths, geocaching, puzzles and problems to solve every day!
A suggestion ? a feedback ? a bug ? an idea ? Write to dCode!
ROT-18 Cipher
ROT18 Decoder
ROT18 Encoder
Answers to Questions (FAQ)
What is ROT-18? (Definition)
ROT-18 is the name given to 2 shift encryption methods, similar to the famous ROT-13 but using the 36 alphanumeric characters.
— Definition 1: Association of ROT-13 and ROT-5 (and 13+5=18), the letters are shifted by 13 (in the 26-letter alphabet ABCDEFGHIJKLMNOPQRSTUVWXYZ) and the numbers by 5 (in the list 0123456789)
— Definition 2: Use of a 36-character alphanumeric alphabet (26 letters and 10 numbers), the characters are then shifted by 18 positions.
These 2 definitions produce different and incompatible results.
How to encrypt using ROT-18 cipher?
To encode by ROT-18, take each character of the message to encode.
— (ROT-13 + ROT-5): Replace the letters (A-Z) with those located 13 positions later in the looping alphabet and replace the numbers (0-9) with those located 5 positions later in the loop
Example: A becomes N, Z becomes M and 0 becomes 5 and 9 becomes 4
— (ROT-18): Replace the characters (A-Z0-9) with those located 18 positions later in the 36-character alphanumeric alphabet: ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789
Non-alphanumeric characters remain unchanged (such as spaces, punctuation or symbols)
How to decrypt ROT-18 cipher?
Decryption is the same as encryption (regardless of the definition used). ROT-18 is a reversible cipher. Decoding involves applying ROT-18 again to the encoded message.
Source code
dCode retains ownership of the "ROT-18 Cipher" source code. Any algorithm for the "ROT-18 Cipher" algorithm, applet or snippet or script (converter, solver, encryption / decryption, encoding / decoding, ciphering / deciphering, breaker, translator), or any "ROT-18 Cipher" functions (calculate, convert, solve, decrypt / encrypt, decipher / cipher, decode / encode, translate) written in any informatic language (Python, Java, PHP, C#, Javascript, Matlab, etc.) or any database download or API access for "ROT-18 Cipher" or any other element are not public (except explicit open source licence). Same with the download for offline use on PC, mobile, tablet, iPhone or Android app.
Reminder: dCode is an educational and teaching resource, accessible online for free and for everyone.
Cite dCode
The content of the page "ROT-18 Cipher" and its results may be freely copied and reused, including for commercial purposes, provided that dCode.fr is cited as the source (Creative Commons CC-BY free distribution license).
Exporting the results is free and can be done simply by clicking on the export icons ⤓ (.csv or .txt format) or ⧉ (copy and paste).
To cite dCode.fr on another website, use the link:
In a scientific article or book, the recommended bibliographic citation is: ROT-18 Cipher on dCode.fr [online website], retrieved on 2025-06-15,
