Which tool is commonly used for cutting in paint along edges?

The most commonly used tool for cutting in paint along edges is a paintbrush. This is primarily because a paintbrush allows for precise control and application of paint, particularly in hard-to-reach areas such as corners, edges of windows, and along trim. The bristles can easily maneuver into crevices and create clean lines, which is crucial for achieving a professional finish.

While rollers are effective for covering large areas quickly, they lack the finesse needed for edges. Paint sprayers are useful for achieving an even coat over wide surfaces but can be challenging to control when it comes to detailed edge work. A putty knife, typically used for scraping or applying substances like spackle or joint compound, is not intended for painting and does not provide the right application technique needed for cutting in. Therefore, the paintbrush stands out as the best choice for this specific task.