A quantum error correction method including correcting a stream of syndrome measurements produced by a quantum computer comprises receiving a layered representation of error propagation through quantum error detection circuits, the layered representation comprises a plurality of line circuit layers that each represent a probability of local detection events in a quantum computer associated with one or more potential error processes in the execution of a quantum algorithm; during execution of the quantum algorithm: receiving one or more syndrome measurements from quantum error detection circuits; converting the syndrome measurements into detection events written to an array that represents a patch of quantum error correction circuits at a sequence of steps in the quantum algorithm; determining one or more errors in the execution of the quantum algorithm from the detection events in dependence upon the stored line circuit layers; and causing correction of the syndrome measurements based on the determined errors.