Perform simple rotational letter substitution (such as ROT-13) in JavaScript.
JavaScript HTML

rot Build status Dependency status

rot is a JavaScript library that performs rotational letter substitution. It can be used to shift any ASCII letters in the input string by a given number of positions in the alphabet. To ROT-13 the string 'abc', for example:

// ROT-13 is the default
// → 'nop'

// Or, specify `13` explicitly:
rot('abc', 13);
// → 'nop'


Via npm:

npm install rot

Via Bower:

bower install rot

Via Component:

component install mathiasbynens/rot

In a browser:

<script src="rot.js"></script>

In Narwhal, Node.js, and RingoJS:

var rot = require('rot');

In Rhino:


Using an AMD loader like RequireJS:

    'paths': {
      'rot': 'path/to/rot'
  function(rot) {



A string representing the semantic version number.

rot(text, [ n = 13 ])

This function takes a string of text and shifts any ASCII letters in the input string by n positions in the alphabet (to the right). The optional n argument defaults to 13. It can be any number from 0 to 26. (Other numeric values are accepted too, but they’re not useful; e.g. ROT-1337 is the same as ROT-11.)

// ROT-13 is the default
// → 'nop'

rot('abc', 13);
// → 'nop'

To decrypt rotational ciphertext for which the n value is known, simply pass 26 - n or just -n as the second parameter to rot(). For example, to decrypt ROT-5:

rot('Ymnx xywnsl nx jshwduyji zxnsl WTY-5.', 26 - 5);
// → 'This string is encrypted using ROT-5.'

rot('Ymnx xywnsl nx jshwduyji zxnsl WTY-5.', -5);
// → 'This string is encrypted using ROT-5.'

Using the rot binary

To use the rot binary in your shell, simply install rot globally using npm:

npm install -g rot

After that you will be able to perform simple rotation encryption from the command line:

$ rot 'foo bar baz'
sbb one onm

$ rot -n 13 'foo bar baz'
sbb one onm

Read a local text file, encrypt it using ROT-5, and save the result to a new file:

$ rot -n 5 < foo.txt > foo-rot-5.txt

Or do the same with an online text file:

$ curl -sL "" | rot -n 5 > rot-5.txt

Or, the opposite — read a local file containing ROT-5 encoded text, decode it back to readable text, and save the result to a new file:

$ rot -n 21 < rot-5.txt > original.txt

See rot --help for the full list of options.


rot is designed to work in at least Node.js v0.10.0, Narwhal 0.3.2, RingoJS 0.8-0.9, PhantomJS 1.9.0, Rhino 1.7RC4, as well as old and modern versions of Chrome, Firefox, Safari, Opera, and Internet Explorer.

Unit tests & code coverage

After cloning this repository, run npm install to install the dependencies needed for he development and testing. You may want to install Istanbul globally using npm install istanbul -g.

Once that’s done, you can run the unit tests in Node using npm test or node tests/tests.js. To run the tests in Rhino, Ringo, Narwhal, and web browsers as well, use grunt test.

To generate the code coverage report, use grunt cover.


Mathias Bynens


rot is available under the MIT license.