An adjustable corner tool is provided having outwardly biased blades. The back surfaces of the blades are connected to an angle control assembly that includes fixed-length arms pivotally connected between each of the blades and a central mounting block. Springs rotationally bias the arms away from each other such that the arms push against the back surfaces of the blades to urge the blades apart. In use, resistive force applied against the front surfaces of the blades moves the blades together. Thus, the adjustable corner tool dynamically adjusts to variations in wall corner angles. The adjustable corner tool can be used with corners in the range of about 160 degrees to 40 degrees and the angle of the tool can also optionally be fixed or maximally limited. In addition, the adjustable corner tool may be adapted to also function as an injection head for delivering spreadable material to a corner.