Checker is one of Auryn's abstract base classes. Any descendant of it is a “checker”. That mean it is an object that performs minimalistic online run-monitoring of your simulation and stops the simulation if something goes wrong. Checkers are called last during the Auryn duty cycle, after the Monitor objects, and can terminate a run in any time step if the run function of the System class is called with the option checking==true (that's the default). When a checker triggers, it might still take MINDELAY time until all other ranks are notified of this run termination, in case a Checker only triggers locally on one rank, which can happen.

The most standard Checker which should be included at least once in every Auryn simulation is the RateChecker. Make sure you define this one first, because Auryn uses the firing estimate of the first Checker to calculate the firing rate value in the progress bar.