An adjustment tool for an external fixator comprises a fitting element for holding fast a clamping assembly of the external fixator. A positioning clamp is provided for fixing the adjustment tool on a rod of the external fixator near the clamping assembly. A connecting element is attached to the fitting element and the positioning clamp is adapted to move the fitting element towards to or away from the positioning clamp. The fitting element comprises a blocking sleeve adapted to push the uppermost jaw of the clamping assembly in the direction of the longitudinal axis of the clamping assembly to block the second upper most jaw against an abutment portion of the fitting element. The tool further comprises an actuation element within the blocking sleeve to actuate the locking element of the clamping assembly for releasing the rod within the clamping assembly without releasing the bone pin.