Counterstring is a Chrome extension developed by eviltesterapps. It falls under the category of Browsers and is classified as an Add-ons & Tools subcategory. This extension provides a simple way to generate CounterStrings, which are strings of text used as test data for testing the length allowed in forms and other data fields.

A CounterString consists of a specific length of characters, with each character preceded by a position number and followed by an asterisk (*). For example, "*3*5*7*9*12*15*" is a CounterString with a length of 15. By examining the CounterString and the position numbers, you can determine if the value has been truncated or not.

CounterStrings are commonly used in exploratory testing. With this extension, you can easily generate CounterStrings by entering the desired number of characters in a dialog. The generated CounterString is then logged to the dev console for easy copying and pasting. Additionally, the CounterString is inserted into the value of the selected input field when the right-click context menu is displayed, making it useful for testing online forms.

Please note that this extension works with forms on the actual page but does not support forms embedded in frames. The source code for Counterstring can be found on GitHub for those interested in exploring its open-source nature.