The master tools are tools that will take your chiptuning to a next level. With the use of a master tool you can completely write and read to the ECU of your vehicle. In comparison to a slave, the master tool can actually replace the software instead of just modifying it. The disadvantage of the master tool is the price. The master tool is almost twice as expensive as the slave. We recommend when you start tuning to use a slave, and if you really want to take a step to the next level you should get yourself a master tool!