Rotter is a Chrome add-on that allows users to speak openly and freely on Twitter using the simple ROT13 cipher. With Rotter, users can encode any words enclosed in square brackets in their tweets, adding an extra layer of obfuscation to their messages. The add-on adds a button to the new tweet form, making it easy to instantly encode the desired words.

In addition to encoding, Rotter also provides a decoding feature. Users can decode any words enclosed in square brackets in tweets they come across. This allows users with the Rotter extension to instantly see the original message, even if it was encoded by another user.

It is important to note that Rotter's ROT13 encryption is not meant to provide any real secrecy or security. It simply shifts each letter along in the alphabet by 13, which can be easily decoded. However, it does provide enough obfuscation to allow users to freely express their thoughts without being impeded.

Rotter is compatible with the Chrome platform and is available for free. It falls under the category of Browsers and the subcategory of Add-ons & Tools. Please note that only plain text should be used within square brackets, without any special characters or URLs.