Connecting device for medium lines

The invention relates to a connecting device (1) for media lines, comprising a coupling element (2), an insert part (3) and a fastening element (4), wherein the coupling element (2) has a connection opening (5) and a fluid channel (6); the insert part (3) can be inserted into the connection opening (5); and the insert part (3) can be fastened to the coupling element (2) by means of the fastening element (4). The connecting device (1) is realized in that the fastening element (4) has at least one control surface (7). When the insert part (3) is inserted into the connection opening (5) under theaction of an installation force, the insert part (3) acts on the control surface (7) in such a way that the fastening element (4) is moved against a restoring force. If the installation force is sufficient, the insert part (3) slides past the control surface (7) and the fastening element (4) interlockingly locks the insert part (3). If the installation force is not sufficient, the fastening element (4) presses the insert