TeaBag: a functional logic debugger. We describe a debugger for functional logic computations. The debugger is an accessory of a virtual machine currently under development. A distinctive feature of this machine is its operational completeness of computations, which places novel demands on a debugger. We give an overview of the debugger’s features, in particular the handling of nondeterminism, the ability to control non-deterministic steps, to remove context information, to toggle eager evaluation, and to set breakpoints on both functions and terms. We briefly describe the debugger’s architecture and its interaction with the associated virtual machine. Finally, we describe a short debugging session of a defective program to show in action debugger features and window screenshots.