Tab Size on GitHub is a Chrome extension developed by Sindre Sorhus. This free add-on falls under the category of Browsers and specifically the subcategory of Add-ons & Tools. The purpose of this extension is to enhance the readability of tab-indented code on GitHub by changing the default tab size from 8 spaces to 4.

By default, web browsers use 8 spaces to represent a tab character, which can make tab-indented code difficult to read. Despite the option to override this default with a more reasonable tab size, GitHub has chosen not to do so. That's where Tab Size on GitHub comes in. This extension ensures that tab-indented code on GitHub is displayed with a tab width of 4, making it easier for developers to navigate and understand the code.