FreePortLocator

FreePortLocator.cs

using System.Net;
using System.Net.Sockets;

public static class FreePortLocator
{
    private static readonly IPEndPoint _defaultLoopbackEndpoint = new(IPAddress.Loopback, port: 0);

    public static int GetAvailablePort()
    {
        using var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        socket.Bind(_defaultLoopbackEndpoint);
        return ((IPEndPoint)socket.LocalEndPoint!).Port;
    }
}