Consider the following:

• For cake-like bars, test with a wooden pick inserted at the center of the pan. If it comes out with a few moist crumbs clinging to it, the cookies are done.
• Chewy (moister) bars will have a dull, rather than shiny, surface; a slight imprint will remain after touching the surface lightly with your fingertip.
• Most bars also pull away slightly from the edges of the pan.