A system for changing and inserting or placing tools on a machine tool, including: a tool changer with a manipulator which is configured to remove a tool to be introduced from a tool magazine of the machine tool at a removal position and to transfer it to a work spindle of the machine tool at a tool change position in an automatic tool changing operation, and a tool diameter measuring apparatus, which is configured to determine a tool diameter or a tool radius of the tool to be introduced that has been removed from the tool magazine of the machine tool by the manipulator.