Abstract: A tool set and a method of opening and decoding a side bar lock employing wafer type tumblers. A spring compressor tool configured for insertion into the lock mechanism keyway raises all the tumblers to a radially outward position and compresses the springs that normally bias the tumblers inwardly. A spring retainer tool inserted into the keyway with the spring compressor tool engages the tumbler springs to retain the springs in a compressed position but frees the tumblers for movement. A tumbler adjusting tool is inserted to grasp the tumblers, and move the tumblers to a position where the lock mechanism can be opened. A decoding tool is inserted to measure the radial position of each tumbler and provide a number which can be used to make a new key. A dust cover holding tool is provided to hold open the spring actuated dust cover.