Marking Knife

A marking knife scores a layout line by severing wood fibers rather than just marking their surface the way a pencil does, leaving a crisp, tearout-free groove that a chisel edge or saw blade can register directly into. Most have a single bevel ground on one face, which lets the flat back ride flush against a square or straightedge for a precisely placed cut, rather than a symmetrical blade that would tend to wander off the line.

It's the standard layout tool anywhere precision joinery is being cut by hand -- a knife line is both more accurate and more durable through the cutting process than a pencil line, which a saw or chisel can obscure or a hand can smudge away before the cut is even made.