Jdrasil: a modular library for computing tree decompositions. While the theoretical aspects concerning the computation of tree width -- one of the most important graph parameters -- are well understood, it is not clear how it can be computed practically. We present the open source Java library Jdrasil that implements several different state of the art algorithms for this task. By experimentally comparing these algorithms, we show that the default choices made in Jdrasil lead to an competitive implementation (it took the third place in the first PACE challenge) while also being easy to use and easy to extend.