r12 is a powerful Chrome add-on designed to enhance layout precision through customizable grid systems. This tool allows users to visualize 12-column, modular, and rule-of-thirds grids on various platforms, including websites and design applications. With a simple one-click activation, designers and developers can easily overlay grids on their work, ensuring clarity and balance in their layouts. The add-on supports responsive mode, allowing users to preview how designs will appear across different devices, such as mobile, tablet, and desktop.

Key features include customizable columns and rows, gutter control, and margin adjustments, which provide flexibility for various design needs. The interface is minimalistic and user-friendly, offering live previews and accessibility options like keyboard navigation. Importantly, r12 is lightweight and does not impact browser performance, while also respecting user privacy by not collecting personal data. This makes it an invaluable tool for anyone focused on creating structured and visually appealing designs.