Here, we present a protocol for quantifying pyramidal neuron hyperexcitability in a mouse model of STXBP1 neurodevelopmental encephalopathy (Stxbp1^hap). We describe steps for preparing brain slices, positioning electrodes, and performing an excitability test to investigate microcircuit failures. This protocol is based on recording layer 2/3 cortical pyramidal neurons in response to stimulation of two independent sets of excitatory axons that recruit feedforward inhibition microcircuits. For complete details on the use and execution of this protocol, please refer to Dos Santos et al.¹