VeriFlow is a novel tool designed to verify network-wide invariants in real-time as the network state evolves. The tool operates as a shim layer between a software-defined networking (SDN) controller and network devices, checking for violations of key network invariants such as the absence of routing loops, black holes, and access control violations. VeriFlow achieves this by slicing the network into equivalence classes of packets, building individual forwarding graphs for each class, and traversing these graphs to determine the status of invariants. The tool uses a custom algorithm to efficiently verify invariants, which has been implemented using a Mininet OpenFlow network and Route Views trace data. Experiments show that VeriFlow can perform rigorous checking within hundreds of microseconds per rule insertion, with minimal impact on network performance and TCP connection setup latency. This makes VeriFlow a promising tool for real-time network debugging and anomaly detection in SDN environments.VeriFlow is a novel tool designed to verify network-wide invariants in real-time as the network state evolves. The tool operates as a shim layer between a software-defined networking (SDN) controller and network devices, checking for violations of key network invariants such as the absence of routing loops, black holes, and access control violations. VeriFlow achieves this by slicing the network into equivalence classes of packets, building individual forwarding graphs for each class, and traversing these graphs to determine the status of invariants. The tool uses a custom algorithm to efficiently verify invariants, which has been implemented using a Mininet OpenFlow network and Route Views trace data. Experiments show that VeriFlow can perform rigorous checking within hundreds of microseconds per rule insertion, with minimal impact on network performance and TCP connection setup latency. This makes VeriFlow a promising tool for real-time network debugging and anomaly detection in SDN environments.