This paper presents a superconducting microstrip photon detector (SMSPD) capable of achieving 10 true photon-number resolution with high fidelity. The detector, which features a large inductance, achieves readout fidelities of 98% for single-photon events and 90% for four- and six-photon events. The detector's design enables real-time photon-number readout through a dual-channel timing setup, reducing data acquisition by three orders of magnitude. The SMSPD's performance is demonstrated through a quantum random-number generator (QRNG) based on sampling the parity of a coherent state, which provides unbiased, robust, and eavesdropping-resistant random numbers. The detector's high fidelity, large dynamic range, and real-time characterization make it a promising solution for optical quantum information science. The study also explores the influence of inductance and width on photon-number resolution, showing that larger inductances and wider strips enhance the detector's performance. The results demonstrate that the SMSPD can resolve up to 10 photons with high fidelity, outperforming traditional methods in terms of efficiency and accuracy. The detector's design and performance have significant implications for quantum communication, quantum computing, and other quantum technologies.This paper presents a superconducting microstrip photon detector (SMSPD) capable of achieving 10 true photon-number resolution with high fidelity. The detector, which features a large inductance, achieves readout fidelities of 98% for single-photon events and 90% for four- and six-photon events. The detector's design enables real-time photon-number readout through a dual-channel timing setup, reducing data acquisition by three orders of magnitude. The SMSPD's performance is demonstrated through a quantum random-number generator (QRNG) based on sampling the parity of a coherent state, which provides unbiased, robust, and eavesdropping-resistant random numbers. The detector's high fidelity, large dynamic range, and real-time characterization make it a promising solution for optical quantum information science. The study also explores the influence of inductance and width on photon-number resolution, showing that larger inductances and wider strips enhance the detector's performance. The results demonstrate that the SMSPD can resolve up to 10 photons with high fidelity, outperforming traditional methods in terms of efficiency and accuracy. The detector's design and performance have significant implications for quantum communication, quantum computing, and other quantum technologies.