A live fiber identifier tool includes a head portion having a slot. A cable containing a pair of optical fibers can be inserted in the slot and forced to bend inside the head portion when a trigger is operated. Any light signal in a given fiber partially leaks from the fiber and exits the cable bend. Two photo detectors are located so that one of the detectors receives more light from the cable bend than the other detector depending on the signal direction in the given fiber. Processing components coupled to the detectors and the indicator define a threshold factor that corresponds to a determined difference between the outputs of the detectors. If the difference between the detector outputs does not exceed the threshold factor, an indicator on the tool reports that light signals are traveling in the pair of optical fibers in opposite directions along the cable.