A holder for a tool for machining a workpiece, wherein the holder comprises a cutting insert receptacle in the region of its front end for receiving a cutting insert and a clamping portion in the region of its opposite rear end for clamping the holder in a machine tool. The cutting insert receptacle comprises an upper and a lower clamping jaw, wherein the holder comprises an upper part on which the upper clamping jaw is arranged, and a lower part on which the lower clamping jaw is arranged. The upper and the lower parts are connected together exclusively by means of a web which extends between a first and a second separating slit, wherein the two separating slits extend between the upper part and the lower part of the holder and are arranged on opposite sides of the web such that the upper part is pivotable relative to the lower part via the web in the manner of a rocker. The first separating slit extends in a front holder region between the cutting insert receptacle and the web. The second separating slit extends in a central holder region between the web and the clamping portion. The holder further comprises an actuating means which cooperates with the upper part in the central holder region and is configured to spread the second separating slit in order to move the upper clamping jaw toward the lower clamping jaw and to clamp the cutting insert between the upper and the lower clamping jaws.