diff --git a/clients/dotnet/MxGateway.Client.Cli/CliArguments.cs b/clients/dotnet/MxGateway.Client.Cli/CliArguments.cs
new file mode 100644
index 0000000..31d6fa0
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client.Cli/CliArguments.cs
@@ -0,0 +1,117 @@
+using System.Globalization;
+
+namespace MxGateway.Client.Cli;
+
+internal sealed class CliArguments
+{
+    private readonly Dictionary<string, string> _values = new(StringComparer.OrdinalIgnoreCase);
+    private readonly HashSet<string> _flags = new(StringComparer.OrdinalIgnoreCase);
+
+    public CliArguments(IEnumerable<string> args)
+    {
+        string? pendingName = null;
+
+        foreach (string arg in args)
+        {
+            if (arg.StartsWith("--", StringComparison.Ordinal))
+            {
+                if (pendingName is not null)
+                {
+                    _flags.Add(pendingName);
+                }
+
+                pendingName = arg[2..];
+                continue;
+            }
+
+            if (pendingName is null)
+            {
+                throw new ArgumentException($"Unexpected argument '{arg}'.");
+            }
+
+            _values[pendingName] = arg;
+            pendingName = null;
+        }
+
+        if (pendingName is not null)
+        {
+            _flags.Add(pendingName);
+        }
+    }
+
+    public bool HasFlag(string name)
+    {
+        return _flags.Contains(name);
+    }
+
+    public string? GetOptional(string name)
+    {
+        return _values.TryGetValue(name, out string? value)
+            ? value
+            : null;
+    }
+
+    public string GetRequired(string name)
+    {
+        string? value = GetOptional(name);
+        if (string.IsNullOrWhiteSpace(value))
+        {
+            throw new ArgumentException($"Missing required option --{name}.");
+        }
+
+        return value;
+    }
+
+    public int GetInt32(string name, int? defaultValue = null)
+    {
+        string? value = GetOptional(name);
+        if (string.IsNullOrWhiteSpace(value))
+        {
+            if (defaultValue.HasValue)
+            {
+                return defaultValue.Value;
+            }
+
+            throw new ArgumentException($"Missing required option --{name}.");
+        }
+
+        return int.Parse(value, CultureInfo.InvariantCulture);
+    }
+
+    public uint GetUInt32(string name, uint defaultValue)
+    {
+        string? value = GetOptional(name);
+        return string.IsNullOrWhiteSpace(value)
+            ? defaultValue
+            : uint.Parse(value, CultureInfo.InvariantCulture);
+    }
+
+    public ulong GetUInt64(string name, ulong defaultValue)
+    {
+        string? value = GetOptional(name);
+        return string.IsNullOrWhiteSpace(value)
+            ? defaultValue
+            : ulong.Parse(value, CultureInfo.InvariantCulture);
+    }
+
+    public TimeSpan GetDuration(string name, TimeSpan defaultValue)
+    {
+        string? value = GetOptional(name);
+        if (string.IsNullOrWhiteSpace(value))
+        {
+            return defaultValue;
+        }
+
+        if (value.EndsWith("ms", StringComparison.OrdinalIgnoreCase))
+        {
+            return TimeSpan.FromMilliseconds(double.Parse(value[..^2], CultureInfo.InvariantCulture));
+        }
+
+        if (value.EndsWith('s'))
+        {
+            return TimeSpan.FromSeconds(double.Parse(value[..^1], CultureInfo.InvariantCulture));
+        }
+
+        return TimeSpan.Parse(value, CultureInfo.InvariantCulture);
+    }
+}
diff --git a/clients/dotnet/MxGateway.Client.Cli/IMxGatewayCliClient.cs b/clients/dotnet/MxGateway.Client.Cli/IMxGatewayCliClient.cs
new file mode 100644
index 0000000..1804341
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client.Cli/IMxGatewayCliClient.cs
@@ -0,0 +1,22 @@
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client.Cli;
+
+public interface IMxGatewayCliClient : IAsyncDisposable
+{
+    Task<OpenSessionReply> OpenSessionAsync(
+        OpenSessionRequest request,
+        CancellationToken cancellationToken);
+
+    Task<CloseSessionReply> CloseSessionAsync(
+        CloseSessionRequest request,
+        CancellationToken cancellationToken);
+
+    Task<MxCommandReply> InvokeAsync(
+        MxCommandRequest request,
+        CancellationToken cancellationToken);
+
+    IAsyncEnumerable<MxEvent> StreamEventsAsync(
+        StreamEventsRequest request,
+        CancellationToken cancellationToken);
+}
diff --git a/clients/dotnet/MxGateway.Client.Cli/MxGatewayCliClientAdapter.cs b/clients/dotnet/MxGateway.Client.Cli/MxGatewayCliClientAdapter.cs
new file mode 100644
index 0000000..f8e8664
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client.Cli/MxGatewayCliClientAdapter.cs
@@ -0,0 +1,40 @@
+using MxGateway.Client;
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client.Cli;
+
+internal sealed class MxGatewayCliClientAdapter(MxGatewayClient client) : IMxGatewayCliClient
+{
+    public Task<OpenSessionReply> OpenSessionAsync(
+        OpenSessionRequest request,
+        CancellationToken cancellationToken)
+    {
+        return client.OpenSessionRawAsync(request, cancellationToken);
+    }
+
+    public Task<CloseSessionReply> CloseSessionAsync(
+        CloseSessionRequest request,
+        CancellationToken cancellationToken)
+    {
+        return client.CloseSessionRawAsync(request, cancellationToken);
+    }
+
+    public Task<MxCommandReply> InvokeAsync(
+        MxCommandRequest request,
+        CancellationToken cancellationToken)
+    {
+        return client.InvokeAsync(request, cancellationToken);
+    }
+
+    public IAsyncEnumerable<MxEvent> StreamEventsAsync(
+        StreamEventsRequest request,
+        CancellationToken cancellationToken)
+    {
+        return client.StreamEventsAsync(request, cancellationToken);
+    }
+
+    public ValueTask DisposeAsync()
+    {
+        return client.DisposeAsync();
+    }
+}
diff --git a/clients/dotnet/MxGateway.Client.Cli/MxGatewayCliSecretRedactor.cs b/clients/dotnet/MxGateway.Client.Cli/MxGatewayCliSecretRedactor.cs
new file mode 100644
index 0000000..42a6a96
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client.Cli/MxGatewayCliSecretRedactor.cs
@@ -0,0 +1,14 @@
+namespace MxGateway.Client.Cli;
+
+internal static class MxGatewayCliSecretRedactor
+{
+    public static string Redact(string value, string? apiKey)
+    {
+        if (string.IsNullOrEmpty(value) || string.IsNullOrEmpty(apiKey))
+        {
+            return value;
+        }
+
+        return value.Replace(apiKey, "[redacted]", StringComparison.Ordinal);
+    }
+}
diff --git a/clients/dotnet/MxGateway.Client.Cli/MxGatewayClientCli.cs b/clients/dotnet/MxGateway.Client.Cli/MxGatewayClientCli.cs
index 8b64cd6..4ba7747 100644
--- a/clients/dotnet/MxGateway.Client.Cli/MxGatewayClientCli.cs
+++ b/clients/dotnet/MxGateway.Client.Cli/MxGatewayClientCli.cs
@@ -1,34 +1,702 @@
+using System.Globalization;
+using System.Text.Json;
+using Google.Protobuf;
 using MxGateway.Client;
+using MxGateway.Contracts.Proto;
 
 namespace MxGateway.Client.Cli;
 
 public static class MxGatewayClientCli
 {
+    private static readonly JsonFormatter ProtobufJsonFormatter = JsonFormatter.Default;
+
+    private static readonly JsonSerializerOptions JsonOptions = new(JsonSerializerDefaults.Web);
+
     public static int Run(
         string[] args,
         TextWriter standardOutput,
         TextWriter standardError)
+    {
+        return RunAsync(args, standardOutput, standardError)
+            .GetAwaiter()
+            .GetResult();
+    }
+
+    public static Task<int> RunAsync(
+        string[] args,
+        TextWriter standardOutput,
+        TextWriter standardError,
+        Func<MxGatewayClientOptions, IMxGatewayCliClient>? clientFactory = null)
     {
         ArgumentNullException.ThrowIfNull(args);
         ArgumentNullException.ThrowIfNull(standardOutput);
         ArgumentNullException.ThrowIfNull(standardError);
 
+        return RunCoreAsync(
+            args,
+            standardOutput,
+            standardError,
+            clientFactory ?? CreateDefaultClient);
+    }
+
+    private static async Task<int> RunCoreAsync(
+        string[] args,
+        TextWriter standardOutput,
+        TextWriter standardError,
+        Func<MxGatewayClientOptions, IMxGatewayCliClient> clientFactory)
+    {
         if (args.Length is 0 || IsHelp(args[0]))
         {
             WriteUsage(standardOutput);
             return 0;
         }
 
-        if (string.Equals(args[0], "version", StringComparison.OrdinalIgnoreCase))
+        string command = args[0].ToLowerInvariant();
+        CliArguments arguments = new(args.Skip(1));
+
+        try
         {
-            standardOutput.WriteLine(
-                $"gateway-protocol={MxGatewayClientContractInfo.GatewayProtocolVersion}");
-            standardOutput.WriteLine(
-                $"worker-protocol={MxGatewayClientContractInfo.WorkerProtocolVersion}");
-            return 0;
+            if (command is "version")
+            {
+                WriteVersion(arguments, standardOutput);
+                return 0;
+            }
+
+            if (!IsKnownGatewayCommand(command))
+            {
+                return WriteUnknownCommand(command, standardError);
+            }
+
+            await using IMxGatewayCliClient client = clientFactory(CreateOptions(arguments));
+            using CancellationTokenSource cancellation = CreateCancellation(arguments);
+
+            return command switch
+            {
+                "open-session" => await OpenSessionAsync(arguments, client, standardOutput, cancellation.Token)
+                    .ConfigureAwait(false),
+                "close-session" => await CloseSessionAsync(arguments, client, standardOutput, cancellation.Token)
+                    .ConfigureAwait(false),
+                "ping" => await PingAsync(arguments, client, standardOutput, cancellation.Token)
+                    .ConfigureAwait(false),
+                "register" => await RegisterAsync(arguments, client, standardOutput, cancellation.Token)
+                    .ConfigureAwait(false),
+                "add-item" => await AddItemAsync(arguments, client, standardOutput, cancellation.Token)
+                    .ConfigureAwait(false),
+                "advise" => await AdviseAsync(arguments, client, standardOutput, cancellation.Token)
+                    .ConfigureAwait(false),
+                "stream-events" => await StreamEventsAsync(arguments, client, standardOutput, cancellation.Token)
+                    .ConfigureAwait(false),
+                "write" => await WriteAsync(arguments, client, standardOutput, cancellation.Token)
+                    .ConfigureAwait(false),
+                "write2" => await Write2Async(arguments, client, standardOutput, cancellation.Token)
+                    .ConfigureAwait(false),
+                "smoke" => await SmokeAsync(arguments, client, standardOutput, cancellation.Token)
+                    .ConfigureAwait(false),
+                _ => WriteUnknownCommand(command, standardError),
+            };
+        }
+        catch (Exception exception) when (exception is not OperationCanceledException)
+        {
+            string? apiKey = arguments.GetOptional("api-key");
+            string message = MxGatewayCliSecretRedactor.Redact(exception.Message, apiKey);
+
+            if (arguments.HasFlag("json"))
+            {
+                standardError.WriteLine(JsonSerializer.Serialize(
+                    new { error = message, type = exception.GetType().Name },
+                    JsonOptions));
+            }
+            else
+            {
+                standardError.WriteLine(message);
+            }
+
+            return 1;
+        }
+    }
+
+    private static IMxGatewayCliClient CreateDefaultClient(MxGatewayClientOptions options)
+    {
+        return new MxGatewayCliClientAdapter(MxGatewayClient.Create(options));
+    }
+
+    private static MxGatewayClientOptions CreateOptions(CliArguments arguments)
+    {
+        string endpoint = arguments.GetOptional("endpoint")
+            ?? Environment.GetEnvironmentVariable("MXGATEWAY_ENDPOINT")
+            ?? "http://localhost:5000";
+
+        string apiKey = ResolveApiKey(arguments);
+
+        return new MxGatewayClientOptions
+        {
+            Endpoint = new Uri(endpoint, UriKind.Absolute),
+            ApiKey = apiKey,
+            UseTls = arguments.HasFlag("tls")
+                || endpoint.StartsWith("https://", StringComparison.OrdinalIgnoreCase),
+            DefaultCallTimeout = arguments.GetDuration("timeout", TimeSpan.FromSeconds(30)),
+            ConnectTimeout = arguments.GetDuration("connect-timeout", TimeSpan.FromSeconds(10)),
+            CaCertificatePath = arguments.GetOptional("ca-file"),
+            ServerNameOverride = arguments.GetOptional("server-name"),
+        };
+    }
+
+    private static string ResolveApiKey(CliArguments arguments)
+    {
+        string? apiKey = arguments.GetOptional("api-key");
+        if (!string.IsNullOrWhiteSpace(apiKey))
+        {
+            return apiKey;
         }
 
-        standardError.WriteLine($"Unknown command '{args[0]}'.");
+        string apiKeyEnvironmentName = arguments.GetOptional("api-key-env")
+            ?? "MXGATEWAY_API_KEY";
+
+        apiKey = Environment.GetEnvironmentVariable(apiKeyEnvironmentName);
+        if (!string.IsNullOrWhiteSpace(apiKey))
+        {
+            return apiKey;
+        }
+
+        throw new ArgumentException(
+            $"Gateway API key is required. Pass --api-key or set {apiKeyEnvironmentName}.");
+    }
+
+    private static CancellationTokenSource CreateCancellation(CliArguments arguments)
+    {
+        var cancellation = new CancellationTokenSource();
+        TimeSpan timeout = arguments.GetDuration("timeout", TimeSpan.FromSeconds(30));
+        cancellation.CancelAfter(timeout);
+        return cancellation;
+    }
+
+    private static Task<int> OpenSessionAsync(
+        CliArguments arguments,
+        IMxGatewayCliClient client,
+        TextWriter output,
+        CancellationToken cancellationToken)
+    {
+        return WriteReplyAsync(
+            client.OpenSessionAsync(
+                new OpenSessionRequest
+                {
+                    ClientSessionName = arguments.GetOptional("client-name") ?? "mxgw-dotnet-cli",
+                    ClientCorrelationId = CreateCorrelationId(),
+                    RequestedBackend = arguments.GetOptional("backend") ?? string.Empty,
+                },
+                cancellationToken),
+            arguments,
+            output);
+    }
+
+    private static Task<int> CloseSessionAsync(
+        CliArguments arguments,
+        IMxGatewayCliClient client,
+        TextWriter output,
+        CancellationToken cancellationToken)
+    {
+        return WriteReplyAsync(
+            client.CloseSessionAsync(
+                new CloseSessionRequest
+                {
+                    SessionId = arguments.GetRequired("session-id"),
+                    ClientCorrelationId = CreateCorrelationId(),
+                },
+                cancellationToken),
+            arguments,
+            output);
+    }
+
+    private static Task<int> PingAsync(
+        CliArguments arguments,
+        IMxGatewayCliClient client,
+        TextWriter output,
+        CancellationToken cancellationToken)
+    {
+        return InvokeAndWriteAsync(
+            arguments,
+            client,
+            output,
+            new MxCommand
+            {
+                Kind = MxCommandKind.Ping,
+                Ping = new PingCommand { Message = arguments.GetOptional("message") ?? "ping" },
+            },
+            cancellationToken);
+    }
+
+    private static Task<int> RegisterAsync(
+        CliArguments arguments,
+        IMxGatewayCliClient client,
+        TextWriter output,
+        CancellationToken cancellationToken)
+    {
+        return InvokeAndWriteAsync(
+            arguments,
+            client,
+            output,
+            new MxCommand
+            {
+                Kind = MxCommandKind.Register,
+                Register = new RegisterCommand { ClientName = arguments.GetOptional("client-name") ?? "mxgw-dotnet-cli" },
+            },
+            cancellationToken);
+    }
+
+    private static Task<int> AddItemAsync(
+        CliArguments arguments,
+        IMxGatewayCliClient client,
+        TextWriter output,
+        CancellationToken cancellationToken)
+    {
+        return InvokeAndWriteAsync(
+            arguments,
+            client,
+            output,
+            new MxCommand
+            {
+                Kind = MxCommandKind.AddItem,
+                AddItem = new AddItemCommand
+                {
+                    ServerHandle = arguments.GetInt32("server-handle"),
+                    ItemDefinition = arguments.GetRequired("item"),
+                },
+            },
+            cancellationToken);
+    }
+
+    private static Task<int> AdviseAsync(
+        CliArguments arguments,
+        IMxGatewayCliClient client,
+        TextWriter output,
+        CancellationToken cancellationToken)
+    {
+        return InvokeAndWriteAsync(
+            arguments,
+            client,
+            output,
+            new MxCommand
+            {
+                Kind = MxCommandKind.Advise,
+                Advise = new AdviseCommand
+                {
+                    ServerHandle = arguments.GetInt32("server-handle"),
+                    ItemHandle = arguments.GetInt32("item-handle"),
+                },
+            },
+            cancellationToken);
+    }
+
+    private static Task<int> WriteAsync(
+        CliArguments arguments,
+        IMxGatewayCliClient client,
+        TextWriter output,
+        CancellationToken cancellationToken)
+    {
+        return InvokeAndWriteAsync(
+            arguments,
+            client,
+            output,
+            new MxCommand
+            {
+                Kind = MxCommandKind.Write,
+                Write = new WriteCommand
+                {
+                    ServerHandle = arguments.GetInt32("server-handle"),
+                    ItemHandle = arguments.GetInt32("item-handle"),
+                    UserId = arguments.GetInt32("user-id", 0),
+                    Value = ParseValue(arguments),
+                },
+            },
+            cancellationToken);
+    }
+
+    private static Task<int> Write2Async(
+        CliArguments arguments,
+        IMxGatewayCliClient client,
+        TextWriter output,
+        CancellationToken cancellationToken)
+    {
+        return InvokeAndWriteAsync(
+            arguments,
+            client,
+            output,
+            new MxCommand
+            {
+                Kind = MxCommandKind.Write2,
+                Write2 = new Write2Command
+                {
+                    ServerHandle = arguments.GetInt32("server-handle"),
+                    ItemHandle = arguments.GetInt32("item-handle"),
+                    UserId = arguments.GetInt32("user-id", 0),
+                    Value = ParseValue(arguments),
+                    TimestampValue = ParseTimestampValue(arguments),
+                },
+            },
+            cancellationToken);
+    }
+
+    private static async Task<int> StreamEventsAsync(
+        CliArguments arguments,
+        IMxGatewayCliClient client,
+        TextWriter output,
+        CancellationToken cancellationToken)
+    {
+        var events = new List<MxEvent>();
+        uint maxEvents = arguments.GetUInt32("max-events", 0);
+        uint eventCount = 0;
+        var request = new StreamEventsRequest
+        {
+            SessionId = arguments.GetRequired("session-id"),
+            AfterWorkerSequence = arguments.GetUInt64("after-worker-sequence", 0),
+        };
+
+        await foreach (MxEvent gatewayEvent in client.StreamEventsAsync(request, cancellationToken)
+            .WithCancellation(cancellationToken)
+            .ConfigureAwait(false))
+        {
+            if (arguments.HasFlag("json"))
+            {
+                events.Add(gatewayEvent);
+            }
+            else
+            {
+                output.WriteLine(ProtobufJsonFormatter.Format(gatewayEvent));
+            }
+
+            eventCount++;
+            if (maxEvents > 0 && eventCount >= maxEvents)
+            {
+                break;
+            }
+        }
+
+        if (arguments.HasFlag("json"))
+        {
+            output.WriteLine(JsonSerializer.Serialize(
+                new { events = events.Select(EventToJsonElement).ToArray() },
+                JsonOptions));
+        }
+
+        return 0;
+    }
+
+    private static async Task<int> SmokeAsync(
+        CliArguments arguments,
+        IMxGatewayCliClient client,
+        TextWriter output,
+        CancellationToken cancellationToken)
+    {
+        OpenSessionReply? openReply = null;
+        CloseSessionReply? closeReply = null;
+        var commandReplies = new List<MxCommandReply>();
+        var events = new List<MxEvent>();
+
+        try
+        {
+            openReply = await client.OpenSessionAsync(
+                    new OpenSessionRequest
+                    {
+                        ClientSessionName = arguments.GetOptional("client-name") ?? "mxgw-dotnet-smoke",
+                        ClientCorrelationId = CreateCorrelationId(),
+                    },
+                    cancellationToken)
+                .ConfigureAwait(false);
+
+            int serverHandle = await InvokeForHandleAsync(
+                    arguments,
+                    client,
+                    openReply.SessionId,
+                    new MxCommand
+                    {
+                        Kind = MxCommandKind.Register,
+                        Register = new RegisterCommand { ClientName = arguments.GetOptional("client-name") ?? "mxgw-dotnet-smoke" },
+                    },
+                    reply => reply.Register?.ServerHandle ?? reply.ReturnValue.Int32Value,
+                    commandReplies,
+                    cancellationToken)
+                .ConfigureAwait(false);
+
+            int itemHandle = await InvokeForHandleAsync(
+                    arguments,
+                    client,
+                    openReply.SessionId,
+                    new MxCommand
+                    {
+                        Kind = MxCommandKind.AddItem,
+                        AddItem = new AddItemCommand
+                        {
+                            ServerHandle = serverHandle,
+                            ItemDefinition = arguments.GetRequired("item"),
+                        },
+                    },
+                    reply => reply.AddItem?.ItemHandle ?? reply.ReturnValue.Int32Value,
+                    commandReplies,
+                    cancellationToken)
+                .ConfigureAwait(false);
+
+            commandReplies.Add(await InvokeAndEnsureAsync(
+                    client,
+                    CreateCommandRequest(
+                        openReply.SessionId,
+                        new MxCommand
+                        {
+                            Kind = MxCommandKind.Advise,
+                            Advise = new AdviseCommand
+                            {
+                                ServerHandle = serverHandle,
+                                ItemHandle = itemHandle,
+                            },
+                        }),
+                    cancellationToken)
+                .ConfigureAwait(false));
+
+            if (arguments.GetOptional("value") is not null)
+            {
+                commandReplies.Add(await InvokeAndEnsureAsync(
+                        client,
+                        CreateCommandRequest(
+                            openReply.SessionId,
+                            new MxCommand
+                            {
+                                Kind = MxCommandKind.Write,
+                                Write = new WriteCommand
+                                {
+                                    ServerHandle = serverHandle,
+                                    ItemHandle = itemHandle,
+                                    UserId = arguments.GetInt32("user-id", 0),
+                                    Value = ParseValue(arguments),
+                                },
+                            }),
+                        cancellationToken)
+                    .ConfigureAwait(false));
+            }
+
+            using CancellationTokenSource streamCancellation = CancellationTokenSource
+                .CreateLinkedTokenSource(cancellationToken);
+            streamCancellation.CancelAfter(arguments.GetDuration(
+                "event-timeout",
+                TimeSpan.FromSeconds(2)));
+
+            try
+            {
+                await foreach (MxEvent gatewayEvent in client.StreamEventsAsync(
+                        new StreamEventsRequest { SessionId = openReply.SessionId },
+                        streamCancellation.Token)
+                    .WithCancellation(streamCancellation.Token)
+                    .ConfigureAwait(false))
+                {
+                    events.Add(gatewayEvent);
+                    if (events.Count >= arguments.GetUInt32("max-events", 1))
+                    {
+                        break;
+                    }
+                }
+            }
+            catch (OperationCanceledException) when (!cancellationToken.IsCancellationRequested)
+            {
+            }
+        }
+        finally
+        {
+            if (openReply is not null)
+            {
+                closeReply = await client.CloseSessionAsync(
+                        new CloseSessionRequest
+                        {
+                            SessionId = openReply.SessionId,
+                            ClientCorrelationId = CreateCorrelationId(),
+                        },
+                        CancellationToken.None)
+                    .ConfigureAwait(false);
+            }
+        }
+
+        WriteSmokeResult(arguments, output, openReply, closeReply, commandReplies, events);
+        return 0;
+    }
+
+    private static async Task<int> InvokeAndWriteAsync(
+        CliArguments arguments,
+        IMxGatewayCliClient client,
+        TextWriter output,
+        MxCommand command,
+        CancellationToken cancellationToken)
+    {
+        MxCommandReply reply = await InvokeAndEnsureAsync(
+                client,
+                CreateCommandRequest(arguments.GetRequired("session-id"), command),
+                cancellationToken)
+            .ConfigureAwait(false);
+
+        WriteMessage(arguments, output, reply);
+        return 0;
+    }
+
+    private static async Task<int> InvokeForHandleAsync(
+        CliArguments arguments,
+        IMxGatewayCliClient client,
+        string sessionId,
+        MxCommand command,
+        Func<MxCommandReply, int> handleSelector,
+        List<MxCommandReply> replies,
+        CancellationToken cancellationToken)
+    {
+        MxCommandReply reply = await InvokeAndEnsureAsync(
+                client,
+                CreateCommandRequest(sessionId, command),
+                cancellationToken)
+            .ConfigureAwait(false);
+        replies.Add(reply);
+        return handleSelector(reply);
+    }
+
+    private static async Task<MxCommandReply> InvokeAndEnsureAsync(
+        IMxGatewayCliClient client,
+        MxCommandRequest request,
+        CancellationToken cancellationToken)
+    {
+        MxCommandReply reply = await client.InvokeAsync(request, cancellationToken)
+            .ConfigureAwait(false);
+        reply.EnsureProtocolSuccess().EnsureMxAccessSuccess();
+        return reply;
+    }
+
+    private static MxCommandRequest CreateCommandRequest(
+        string sessionId,
+        MxCommand command)
+    {
+        return new MxCommandRequest
+        {
+            SessionId = sessionId,
+            ClientCorrelationId = CreateCorrelationId(),
+            Command = command,
+        };
+    }
+
+    private static async Task<int> WriteReplyAsync<TReply>(
+        Task<TReply> replyTask,
+        CliArguments arguments,
+        TextWriter output)
+        where TReply : IMessage
+    {
+        TReply reply = await replyTask.ConfigureAwait(false);
+        WriteMessage(arguments, output, reply);
+        return 0;
+    }
+
+    private static void WriteVersion(CliArguments arguments, TextWriter output)
+    {
+        if (arguments.HasFlag("json"))
+        {
+            output.WriteLine(JsonSerializer.Serialize(
+                new
+                {
+                    gatewayProtocolVersion = MxGatewayClientContractInfo.GatewayProtocolVersion,
+                    workerProtocolVersion = MxGatewayClientContractInfo.WorkerProtocolVersion,
+                },
+                JsonOptions));
+            return;
+        }
+
+        output.WriteLine(
+            $"gateway-protocol={MxGatewayClientContractInfo.GatewayProtocolVersion}");
+        output.WriteLine(
+            $"worker-protocol={MxGatewayClientContractInfo.WorkerProtocolVersion}");
+    }
+
+    private static void WriteMessage(
+        CliArguments arguments,
+        TextWriter output,
+        IMessage message)
+    {
+        output.WriteLine(arguments.HasFlag("json")
+            ? ProtobufJsonFormatter.Format(message)
+            : message.ToString());
+    }
+
+    private static void WriteSmokeResult(
+        CliArguments arguments,
+        TextWriter output,
+        OpenSessionReply? openReply,
+        CloseSessionReply? closeReply,
+        IReadOnlyList<MxCommandReply> commandReplies,
+        IReadOnlyList<MxEvent> events)
+    {
+        if (!arguments.HasFlag("json"))
+        {
+            output.WriteLine($"session-id={openReply?.SessionId}");
+            output.WriteLine($"commands={commandReplies.Count}");
+            output.WriteLine($"events={events.Count}");
+            output.WriteLine($"closed={closeReply is not null}");
+            return;
+        }
+
+        output.WriteLine(JsonSerializer.Serialize(
+            new
+            {
+                sessionId = openReply?.SessionId,
+                closed = closeReply is not null,
+                commandReplies = commandReplies.Select(CommandReplyToJsonElement).ToArray(),
+                events = events.Select(EventToJsonElement).ToArray(),
+            },
+            JsonOptions));
+    }
+
+    private static JsonElement CommandReplyToJsonElement(MxCommandReply reply)
+    {
+        return JsonDocument.Parse(ProtobufJsonFormatter.Format(reply)).RootElement.Clone();
+    }
+
+    private static JsonElement EventToJsonElement(MxEvent gatewayEvent)
+    {
+        return JsonDocument.Parse(ProtobufJsonFormatter.Format(gatewayEvent)).RootElement.Clone();
+    }
+
+    private static MxValue ParseValue(CliArguments arguments)
+    {
+        string type = arguments.GetRequired("type").ToLowerInvariant();
+        string value = arguments.GetRequired("value");
+        string[] values = value.Split(',', StringSplitOptions.TrimEntries);
+
+        return type switch
+        {
+            "bool" or "boolean" => bool.Parse(value).ToMxValue(),
+            "bool-array" or "boolean-array" => values.Select(bool.Parse).ToArray().ToMxValue(),
+            "int32" or "integer" => int.Parse(value, CultureInfo.InvariantCulture).ToMxValue(),
+            "int32-array" or "integer-array" => values.Select(item => int.Parse(item, CultureInfo.InvariantCulture)).ToArray().ToMxValue(),
+            "int64" => long.Parse(value, CultureInfo.InvariantCulture).ToMxValue(),
+            "int64-array" => values.Select(item => long.Parse(item, CultureInfo.InvariantCulture)).ToArray().ToMxValue(),
+            "float" => float.Parse(value, CultureInfo.InvariantCulture).ToMxValue(),
+            "float-array" => values.Select(item => float.Parse(item, CultureInfo.InvariantCulture)).ToArray().ToMxValue(),
+            "double" => double.Parse(value, CultureInfo.InvariantCulture).ToMxValue(),
+            "double-array" => values.Select(item => double.Parse(item, CultureInfo.InvariantCulture)).ToArray().ToMxValue(),
+            "string" => value.ToMxValue(),
+            "string-array" => values.ToMxValue(),
+            "time" or "timestamp" => DateTimeOffset.Parse(value, CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal).ToMxValue(),
+            "time-array" or "timestamp-array" => values
+                .Select(item => DateTimeOffset.Parse(item, CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal))
+                .ToArray()
+                .ToMxValue(),
+            _ => throw new ArgumentException($"Unsupported MX value type '{type}'."),
+        };
+    }
+
+    private static MxValue ParseTimestampValue(CliArguments arguments)
+    {
+        string timestamp = arguments.GetOptional("timestamp")
+            ?? DateTimeOffset.UtcNow.ToString("O", CultureInfo.InvariantCulture);
+
+        return DateTimeOffset.Parse(
+                timestamp,
+                CultureInfo.InvariantCulture,
+                DateTimeStyles.AssumeUniversal)
+            .ToMxValue();
+    }
+
+    private static int WriteUnknownCommand(string command, TextWriter standardError)
+    {
+        standardError.WriteLine($"Unknown command '{command}'.");
         WriteUsage(standardError);
         return 2;
     }
@@ -40,9 +708,37 @@ public static class MxGatewayClientCli
             || string.Equals(value, "help", StringComparison.OrdinalIgnoreCase);
     }
 
+    private static bool IsKnownGatewayCommand(string command)
+    {
+        return command is "open-session"
+            or "close-session"
+            or "ping"
+            or "register"
+            or "add-item"
+            or "advise"
+            or "stream-events"
+            or "write"
+            or "write2"
+            or "smoke";
+    }
+
+    private static string CreateCorrelationId()
+    {
+        return Guid.NewGuid().ToString("N");
+    }
+
     private static void WriteUsage(TextWriter writer)
     {
-        writer.WriteLine("mxgw-dotnet version");
-        writer.WriteLine("mxgw-dotnet --help");
+        writer.WriteLine("mxgw-dotnet version [--json]");
+        writer.WriteLine("mxgw-dotnet ping --session-id <id> [--json]");
+        writer.WriteLine("mxgw-dotnet open-session [--client-name <name>] [--json]");
+        writer.WriteLine("mxgw-dotnet close-session --session-id <id> [--json]");
+        writer.WriteLine("mxgw-dotnet register --session-id <id> --client-name <name> [--json]");
+        writer.WriteLine("mxgw-dotnet add-item --session-id <id> --server-handle <n> --item <ref> [--json]");
+        writer.WriteLine("mxgw-dotnet advise --session-id <id> --server-handle <n> --item-handle <n> [--json]");
+        writer.WriteLine("mxgw-dotnet stream-events --session-id <id> [--max-events <n>] [--json]");
+        writer.WriteLine("mxgw-dotnet write --session-id <id> --server-handle <n> --item-handle <n> --type <type> --value <value> [--json]");
+        writer.WriteLine("mxgw-dotnet write2 --session-id <id> --server-handle <n> --item-handle <n> --type <type> --value <value> [--timestamp <iso>] [--json]");
+        writer.WriteLine("mxgw-dotnet smoke --item <ref> [--value <value> --type <type>] [--json]");
     }
 }
diff --git a/clients/dotnet/MxGateway.Client.Cli/Program.cs b/clients/dotnet/MxGateway.Client.Cli/Program.cs
index 3f1db75..fbea43f 100644
--- a/clients/dotnet/MxGateway.Client.Cli/Program.cs
+++ b/clients/dotnet/MxGateway.Client.Cli/Program.cs
@@ -1,3 +1,3 @@
 using MxGateway.Client.Cli;
 
-return MxGatewayClientCli.Run(args, Console.Out, Console.Error);
+return await MxGatewayClientCli.RunAsync(args, Console.Out, Console.Error);
diff --git a/clients/dotnet/MxGateway.Client.Tests/MxCommandReplyExtensionsTests.cs b/clients/dotnet/MxGateway.Client.Tests/MxCommandReplyExtensionsTests.cs
new file mode 100644
index 0000000..686c1e4
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client.Tests/MxCommandReplyExtensionsTests.cs
@@ -0,0 +1,78 @@
+using Google.Protobuf;
+using MxGateway.Client;
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client.Tests;
+
+public sealed class MxCommandReplyExtensionsTests
+{
+    [Fact]
+    public void EnsureSuccess_WithRegisterFixture_ReturnsReply()
+    {
+        MxCommandReply reply = ReadReplyFixture("register.ok.reply.json");
+
+        Assert.Same(reply, reply.EnsureProtocolSuccess());
+        Assert.Same(reply, reply.EnsureMxAccessSuccess());
+    }
+
+    [Fact]
+    public void EnsureMxAccessSuccess_WithFailureFixture_PreservesHResultAndStatuses()
+    {
+        MxCommandReply reply = ReadReplyFixture("write.mxaccess-failure.reply.json");
+
+        reply.EnsureProtocolSuccess();
+        MxAccessException exception = Assert.Throws<MxAccessException>(
+            reply.EnsureMxAccessSuccess);
+
+        Assert.Equal(-2147220992, exception.HResultCode);
+        Assert.Equal(reply.Statuses.Count, exception.Statuses.Count);
+        Assert.Equal(reply, exception.Reply);
+        Assert.Contains("0x80040200", exception.Message);
+    }
+
+    [Fact]
+    public void EnsureProtocolSuccess_WithSessionFailure_ThrowsSessionException()
+    {
+        MxCommandReply reply = new()
+        {
+            SessionId = "session-missing",
+            CorrelationId = "correlation",
+            ProtocolStatus = new ProtocolStatus
+            {
+                Code = ProtocolStatusCode.SessionNotFound,
+                Message = "Session was not found.",
+            },
+        };
+
+        MxGatewaySessionException exception = Assert.Throws<MxGatewaySessionException>(
+            reply.EnsureProtocolSuccess);
+
+        Assert.Equal("session-missing", exception.SessionId);
+        Assert.Equal(ProtocolStatusCode.SessionNotFound, exception.ProtocolStatus?.Code);
+    }
+
+    private static MxCommandReply ReadReplyFixture(string fileName)
+    {
+        DirectoryInfo directory = new(AppContext.BaseDirectory);
+        while (directory is not null)
+        {
+            string path = Path.Combine(
+                directory.FullName,
+                "clients",
+                "proto",
+                "fixtures",
+                "behavior",
+                "command-replies",
+                fileName);
+
+            if (File.Exists(path))
+            {
+                return JsonParser.Default.Parse<MxCommandReply>(File.ReadAllText(path));
+            }
+
+            directory = directory.Parent!;
+        }
+
+        throw new FileNotFoundException(fileName);
+    }
+}
diff --git a/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientCliTests.cs b/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientCliTests.cs
index 5ee9ebc..cddc1d1 100644
--- a/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientCliTests.cs
+++ b/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientCliTests.cs
@@ -1,4 +1,5 @@
 using MxGateway.Client.Cli;
+using MxGateway.Contracts.Proto;
 
 namespace MxGateway.Client.Tests;
 
@@ -17,4 +18,224 @@ public sealed class MxGatewayClientCliTests
         Assert.Contains("worker-protocol=1", output.ToString());
         Assert.Equal(string.Empty, error.ToString());
     }
+
+    [Fact]
+    public async Task RunAsync_VersionJson_PrintsJsonProtocolVersions()
+    {
+        using var output = new StringWriter();
+        using var error = new StringWriter();
+
+        int exitCode = await MxGatewayClientCli.RunAsync(["version", "--json"], output, error);
+
+        Assert.Equal(0, exitCode);
+        Assert.Contains("\"gatewayProtocolVersion\":1", output.ToString());
+        Assert.Equal(string.Empty, error.ToString());
+    }
+
+    [Fact]
+    public async Task RunAsync_Write_BuildsWriteCommandAndPrintsJsonReply()
+    {
+        using var output = new StringWriter();
+        using var error = new StringWriter();
+        FakeCliClient fakeClient = new();
+        fakeClient.InvokeReplies.Enqueue(new MxCommandReply
+        {
+            SessionId = "session-fixture",
+            Kind = MxCommandKind.Write,
+            ProtocolStatus = new ProtocolStatus { Code = ProtocolStatusCode.Ok },
+        });
+
+        int exitCode = await MxGatewayClientCli.RunAsync(
+            [
+                "write",
+                "--endpoint",
+                "http://localhost:5000",
+                "--api-key",
+                "test-api-key",
+                "--session-id",
+                "session-fixture",
+                "--server-handle",
+                "12",
+                "--item-handle",
+                "34",
+                "--type",
+                "int32",
+                "--value",
+                "123",
+                "--json",
+            ],
+            output,
+            error,
+            _ => fakeClient);
+
+        Assert.Equal(0, exitCode);
+        MxCommandRequest request = Assert.Single(fakeClient.InvokeRequests);
+        Assert.Equal(MxCommandKind.Write, request.Command.Kind);
+        Assert.Equal(123, request.Command.Write.Value.Int32Value);
+        Assert.Contains("MX_COMMAND_KIND_WRITE", output.ToString());
+        Assert.Equal(string.Empty, error.ToString());
+    }
+
+    [Fact]
+    public async Task RunAsync_ErrorOutput_RedactsApiKey()
+    {
+        using var output = new StringWriter();
+        using var error = new StringWriter();
+
+        int exitCode = await MxGatewayClientCli.RunAsync(
+            [
+                "open-session",
+                "--endpoint",
+                "http://localhost:5000",
+                "--api-key",
+                "secret-api-key",
+            ],
+            output,
+            error,
+            _ => throw new InvalidOperationException("boom secret-api-key"));
+
+        Assert.Equal(1, exitCode);
+        Assert.DoesNotContain("secret-api-key", error.ToString());
+        Assert.Contains("[redacted]", error.ToString());
+    }
+
+    [Fact]
+    public async Task RunAsync_StreamEvents_WithMaxEventsStopsNonJsonOutput()
+    {
+        using var output = new StringWriter();
+        using var error = new StringWriter();
+        FakeCliClient fakeClient = new();
+        fakeClient.Events.Add(new MxEvent
+        {
+            SessionId = "session-fixture",
+            Family = MxEventFamily.OnDataChange,
+            WorkerSequence = 1,
+        });
+        fakeClient.Events.Add(new MxEvent
+        {
+            SessionId = "session-fixture",
+            Family = MxEventFamily.OnWriteComplete,
+            WorkerSequence = 2,
+        });
+
+        int exitCode = await MxGatewayClientCli.RunAsync(
+            [
+                "stream-events",
+                "--endpoint",
+                "http://localhost:5000",
+                "--api-key",
+                "test-api-key",
+                "--session-id",
+                "session-fixture",
+                "--max-events",
+                "1",
+            ],
+            output,
+            error,
+            _ => fakeClient);
+
+        Assert.Equal(0, exitCode);
+        Assert.Contains("workerSequence", output.ToString());
+        Assert.DoesNotContain("ON_WRITE_COMPLETE", output.ToString());
+    }
+
+
+    [Fact]
+    public async Task RunAsync_Smoke_WhenCommandFails_ClosesOpenedSession()
+    {
+        using var output = new StringWriter();
+        using var error = new StringWriter();
+        FakeCliClient fakeClient = new()
+        {
+            InvokeFailure = new InvalidOperationException("register failed"),
+        };
+
+        int exitCode = await MxGatewayClientCli.RunAsync(
+            [
+                "smoke",
+                "--endpoint",
+                "http://localhost:5000",
+                "--api-key",
+                "test-api-key",
+                "--item",
+                "Area001.Pump001.Speed",
+                "--json",
+            ],
+            output,
+            error,
+            _ => fakeClient);
+
+        Assert.Equal(1, exitCode);
+        CloseSessionRequest closeRequest = Assert.Single(fakeClient.CloseSessionRequests);
+        Assert.Equal("session-fixture", closeRequest.SessionId);
+    }
+
+    private sealed class FakeCliClient : IMxGatewayCliClient
+    {
+        public Queue<MxCommandReply> InvokeReplies { get; } = new();
+
+        public List<MxCommandRequest> InvokeRequests { get; } = [];
+
+        public List<CloseSessionRequest> CloseSessionRequests { get; } = [];
+
+        public List<MxEvent> Events { get; } = [];
+
+        public Exception? InvokeFailure { get; init; }
+
+        public ValueTask DisposeAsync()
+        {
+            return ValueTask.CompletedTask;
+        }
+
+        public Task<OpenSessionReply> OpenSessionAsync(
+            OpenSessionRequest request,
+            CancellationToken cancellationToken)
+        {
+            return Task.FromResult(new OpenSessionReply
+            {
+                SessionId = "session-fixture",
+                ProtocolStatus = new ProtocolStatus { Code = ProtocolStatusCode.Ok },
+                GatewayProtocolVersion = 1,
+                WorkerProtocolVersion = 1,
+            });
+        }
+
+        public Task<CloseSessionReply> CloseSessionAsync(
+            CloseSessionRequest request,
+            CancellationToken cancellationToken)
+        {
+            CloseSessionRequests.Add(request);
+            return Task.FromResult(new CloseSessionReply
+            {
+                SessionId = request.SessionId,
+                ProtocolStatus = new ProtocolStatus { Code = ProtocolStatusCode.Ok },
+                FinalState = SessionState.Closed,
+            });
+        }
+
+        public Task<MxCommandReply> InvokeAsync(
+            MxCommandRequest request,
+            CancellationToken cancellationToken)
+        {
+            InvokeRequests.Add(request);
+            if (InvokeFailure is not null)
+            {
+                throw InvokeFailure;
+            }
+
+            return Task.FromResult(InvokeReplies.Dequeue());
+        }
+
+        public async IAsyncEnumerable<MxEvent> StreamEventsAsync(
+            StreamEventsRequest request,
+            [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken)
+        {
+            foreach (MxEvent gatewayEvent in Events)
+            {
+                cancellationToken.ThrowIfCancellationRequested();
+                await Task.Yield();
+                yield return gatewayEvent;
+            }
+        }
+    }
 }
diff --git a/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientSessionTests.cs b/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientSessionTests.cs
index 3248c51..2cb36d3 100644
--- a/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientSessionTests.cs
+++ b/clients/dotnet/MxGateway.Client.Tests/MxGatewayClientSessionTests.cs
@@ -110,6 +110,33 @@ public sealed class MxGatewayClientSessionTests
         Assert.Equal(56, request.Command.Write.UserId);
     }
 
+    [Fact]
+    public async Task Write2RawAsync_BuildsWrite2CommandWithValueAndTimestamp()
+    {
+        FakeGatewayTransport transport = CreateTransport();
+        transport.AddInvokeReply(new MxCommandReply
+        {
+            SessionId = "session-fixture",
+            Kind = MxCommandKind.Write2,
+            ProtocolStatus = new ProtocolStatus { Code = ProtocolStatusCode.Ok },
+        });
+        await using MxGatewayClient client = CreateClient(transport);
+        MxGatewaySession session = await client.OpenSessionAsync();
+        MxValue value = 123.ToMxValue();
+        MxValue timestampValue = DateTimeOffset.Parse("2026-01-01T00:00:00Z").ToMxValue();
+
+        MxCommandReply reply = await session.Write2RawAsync(12, 34, value, timestampValue, 56);
+
+        Assert.Equal(MxCommandKind.Write2, reply.Kind);
+        MxCommandRequest request = Assert.Single(transport.InvokeCalls).Request;
+        Assert.Equal(MxCommandKind.Write2, request.Command.Kind);
+        Assert.Equal(12, request.Command.Write2.ServerHandle);
+        Assert.Equal(34, request.Command.Write2.ItemHandle);
+        Assert.Same(value, request.Command.Write2.Value);
+        Assert.Same(timestampValue, request.Command.Write2.TimestampValue);
+        Assert.Equal(56, request.Command.Write2.UserId);
+    }
+
     [Fact]
     public async Task StreamEventsAsync_YieldsEventsInGatewayOrder()
     {
diff --git a/clients/dotnet/MxGateway.Client.Tests/MxStatusProxyExtensionsTests.cs b/clients/dotnet/MxGateway.Client.Tests/MxStatusProxyExtensionsTests.cs
new file mode 100644
index 0000000..76ecca8
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client.Tests/MxStatusProxyExtensionsTests.cs
@@ -0,0 +1,57 @@
+using System.Text.Json;
+using Google.Protobuf;
+using MxGateway.Client;
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client.Tests;
+
+public sealed class MxStatusProxyExtensionsTests
+{
+    [Fact]
+    public void FixtureStatuses_ProjectSuccessAndPreserveRawFields()
+    {
+        using JsonDocument document = JsonDocument.Parse(ReadFixture(
+            "statuses",
+            "status-conversion-cases.json"));
+
+        foreach (JsonElement testCase in document.RootElement.GetProperty("cases").EnumerateArray())
+        {
+            MxStatusProxy status = JsonParser.Default.Parse<MxStatusProxy>(
+                testCase.GetProperty("status").GetRawText());
+            int success = testCase.GetProperty("status").GetProperty("success").GetInt32();
+
+            Assert.Equal(success != 0 && status.Category is MxStatusCategory.Ok, status.IsSuccess());
+            Assert.Equal(
+                testCase.GetProperty("status").GetProperty("rawCategory").GetInt32(),
+                status.RawCategory);
+            Assert.Equal(
+                testCase.GetProperty("status").GetProperty("rawDetectedBy").GetInt32(),
+                status.RawDetectedBy);
+        }
+    }
+
+    private static string ReadFixture(string category, string fileName)
+    {
+        DirectoryInfo directory = new(AppContext.BaseDirectory);
+        while (directory is not null)
+        {
+            string path = Path.Combine(
+                directory.FullName,
+                "clients",
+                "proto",
+                "fixtures",
+                "behavior",
+                category,
+                fileName);
+
+            if (File.Exists(path))
+            {
+                return File.ReadAllText(path);
+            }
+
+            directory = directory.Parent!;
+        }
+
+        throw new FileNotFoundException(fileName);
+    }
+}
diff --git a/clients/dotnet/MxGateway.Client.Tests/MxValueExtensionsTests.cs b/clients/dotnet/MxGateway.Client.Tests/MxValueExtensionsTests.cs
new file mode 100644
index 0000000..2fbde41
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client.Tests/MxValueExtensionsTests.cs
@@ -0,0 +1,79 @@
+using System.Text.Json;
+using Google.Protobuf;
+using MxGateway.Client;
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client.Tests;
+
+public sealed class MxValueExtensionsTests
+{
+    [Fact]
+    public void ToMxValue_WithScalarValues_CreatesTypedProtobufValues()
+    {
+        Assert.Equal(MxValue.KindOneofCase.BoolValue, true.ToMxValue().KindCase);
+        Assert.Equal(MxValue.KindOneofCase.Int32Value, 123.ToMxValue().KindCase);
+        Assert.Equal(MxValue.KindOneofCase.Int64Value, 123L.ToMxValue().KindCase);
+        Assert.Equal(MxValue.KindOneofCase.FloatValue, 1.25F.ToMxValue().KindCase);
+        Assert.Equal(MxValue.KindOneofCase.DoubleValue, 2.5D.ToMxValue().KindCase);
+        Assert.Equal(MxValue.KindOneofCase.StringValue, "alpha".ToMxValue().KindCase);
+    }
+
+    [Fact]
+    public void ToMxValue_WithArrays_CreatesTypedArrayProtobufValues()
+    {
+        MxValue value = new[] { "alpha", "beta" }.ToMxValue();
+
+        Assert.Equal(MxValue.KindOneofCase.ArrayValue, value.KindCase);
+        Assert.Equal(MxArray.ValuesOneofCase.StringValues, value.ArrayValue.ValuesCase);
+        Assert.Equal(["alpha", "beta"], value.ArrayValue.StringValues.Values);
+        Assert.Equal([2U], value.ArrayValue.Dimensions);
+    }
+
+    [Fact]
+    public void FixtureValues_ProjectExpectedKindsAndPreserveRawMetadata()
+    {
+        using JsonDocument document = JsonDocument.Parse(ReadFixture(
+            "values",
+            "value-conversion-cases.json"));
+
+        foreach (JsonElement testCase in document.RootElement.GetProperty("cases").EnumerateArray())
+        {
+            string expectedKind = testCase.GetProperty("expectedKind").GetString()!;
+            MxValue value = JsonParser.Default.Parse<MxValue>(
+                testCase.GetProperty("value").GetRawText());
+
+            Assert.Equal(expectedKind, value.GetProjectionKind());
+
+            if (testCase.GetProperty("id").GetString() is "raw-fallback.variant")
+            {
+                Assert.Equal(32767, value.RawDataType);
+                Assert.Equal([1, 2, 3, 4, 5], Assert.IsType<byte[]>(value.ToClrValue()));
+            }
+        }
+    }
+
+    private static string ReadFixture(string category, string fileName)
+    {
+        DirectoryInfo directory = new(AppContext.BaseDirectory);
+        while (directory is not null)
+        {
+            string path = Path.Combine(
+                directory.FullName,
+                "clients",
+                "proto",
+                "fixtures",
+                "behavior",
+                category,
+                fileName);
+
+            if (File.Exists(path))
+            {
+                return File.ReadAllText(path);
+            }
+
+            directory = directory.Parent!;
+        }
+
+        throw new FileNotFoundException(fileName);
+    }
+}
diff --git a/clients/dotnet/MxGateway.Client/GrpcMxGatewayClientTransport.cs b/clients/dotnet/MxGateway.Client/GrpcMxGatewayClientTransport.cs
index 3bc9e85..6db23ed 100644
--- a/clients/dotnet/MxGateway.Client/GrpcMxGatewayClientTransport.cs
+++ b/clients/dotnet/MxGateway.Client/GrpcMxGatewayClientTransport.cs
@@ -17,27 +17,48 @@ internal sealed class GrpcMxGatewayClientTransport(
         OpenSessionRequest request,
         CallOptions callOptions)
     {
-        return await RawClient.OpenSessionAsync(request, callOptions)
-            .ResponseAsync
-            .ConfigureAwait(false);
+        try
+        {
+            return await RawClient.OpenSessionAsync(request, callOptions)
+                .ResponseAsync
+                .ConfigureAwait(false);
+        }
+        catch (RpcException exception)
+        {
+            throw MapRpcException(exception);
+        }
     }
 
     public async Task<CloseSessionReply> CloseSessionAsync(
         CloseSessionRequest request,
         CallOptions callOptions)
     {
-        return await RawClient.CloseSessionAsync(request, callOptions)
-            .ResponseAsync
-            .ConfigureAwait(false);
+        try
+        {
+            return await RawClient.CloseSessionAsync(request, callOptions)
+                .ResponseAsync
+                .ConfigureAwait(false);
+        }
+        catch (RpcException exception)
+        {
+            throw MapRpcException(exception);
+        }
     }
 
     public async Task<MxCommandReply> InvokeAsync(
         MxCommandRequest request,
         CallOptions callOptions)
     {
-        return await RawClient.InvokeAsync(request, callOptions)
-            .ResponseAsync
-            .ConfigureAwait(false);
+        try
+        {
+            return await RawClient.InvokeAsync(request, callOptions)
+                .ResponseAsync
+                .ConfigureAwait(false);
+        }
+        catch (RpcException exception)
+        {
+            throw MapRpcException(exception);
+        }
     }
 
     public async IAsyncEnumerable<MxEvent> StreamEventsAsync(
@@ -51,10 +72,24 @@ internal sealed class GrpcMxGatewayClientTransport(
 
         using AsyncServerStreamingCall<MxEvent> call = RawClient.StreamEvents(request, callOptions);
 
-        await foreach (MxEvent gatewayEvent in call.ResponseStream
-            .ReadAllAsync(effectiveCancellationToken)
-            .ConfigureAwait(false))
+        IAsyncStreamReader<MxEvent> responseStream = call.ResponseStream;
+        while (true)
         {
+            MxEvent? gatewayEvent;
+            try
+            {
+                if (!await responseStream.MoveNext(effectiveCancellationToken).ConfigureAwait(false))
+                {
+                    break;
+                }
+
+                gatewayEvent = responseStream.Current;
+            }
+            catch (RpcException exception)
+            {
+                throw MapRpcException(exception);
+            }
+
             yield return gatewayEvent;
         }
     }
@@ -65,4 +100,18 @@ internal sealed class GrpcMxGatewayClientTransport(
     {
         return StreamEventsAsync(request, callOptions);
     }
+
+    private static MxGatewayException MapRpcException(RpcException exception)
+    {
+        return exception.StatusCode switch
+        {
+            StatusCode.Unauthenticated => new MxGatewayAuthenticationException(
+                exception.Status.Detail,
+                innerException: exception),
+            StatusCode.PermissionDenied => new MxGatewayAuthorizationException(
+                exception.Status.Detail,
+                innerException: exception),
+            _ => new MxGatewayException(exception.Status.Detail, exception),
+        };
+    }
 }
diff --git a/clients/dotnet/MxGateway.Client/MxAccessException.cs b/clients/dotnet/MxGateway.Client/MxAccessException.cs
new file mode 100644
index 0000000..a2a14ca
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client/MxAccessException.cs
@@ -0,0 +1,24 @@
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client;
+
+public sealed class MxAccessException : MxGatewayCommandException
+{
+    public MxAccessException(
+        string message,
+        MxCommandReply reply,
+        Exception? innerException = null)
+        : base(
+            message,
+            reply.SessionId,
+            reply.CorrelationId,
+            reply.ProtocolStatus,
+            reply.HasHresult ? reply.Hresult : null,
+            reply.Statuses.ToArray(),
+            innerException)
+    {
+        Reply = reply;
+    }
+
+    public MxCommandReply Reply { get; }
+}
diff --git a/clients/dotnet/MxGateway.Client/MxCommandReplyExtensions.cs b/clients/dotnet/MxGateway.Client/MxCommandReplyExtensions.cs
new file mode 100644
index 0000000..ce9f2b8
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client/MxCommandReplyExtensions.cs
@@ -0,0 +1,96 @@
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client;
+
+public static class MxCommandReplyExtensions
+{
+    public static MxCommandReply EnsureProtocolSuccess(this MxCommandReply reply)
+    {
+        ArgumentNullException.ThrowIfNull(reply);
+
+        ProtocolStatusCode code = reply.ProtocolStatus?.Code
+            ?? ProtocolStatusCode.Unspecified;
+
+        if (code is ProtocolStatusCode.Ok or ProtocolStatusCode.MxaccessFailure)
+        {
+            return reply;
+        }
+
+        throw CreateProtocolException(reply, code);
+    }
+
+    public static MxCommandReply EnsureMxAccessSuccess(this MxCommandReply reply)
+    {
+        ArgumentNullException.ThrowIfNull(reply);
+
+        bool mxAccessFailure = reply.ProtocolStatus?.Code is ProtocolStatusCode.MxaccessFailure;
+        bool hResultFailure = reply.HasHresult && reply.Hresult != 0;
+        bool statusFailure = reply.Statuses.Any(status => !status.IsSuccess());
+
+        if (!mxAccessFailure && !hResultFailure && !statusFailure)
+        {
+            return reply;
+        }
+
+        throw new MxAccessException(CreateMxAccessMessage(reply), reply);
+    }
+
+    private static MxGatewayException CreateProtocolException(
+        MxCommandReply reply,
+        ProtocolStatusCode code)
+    {
+        string message = CreateProtocolMessage(reply);
+        int? hResult = reply.HasHresult ? reply.Hresult : null;
+        MxStatusProxy[] statuses = reply.Statuses.ToArray();
+
+        return code switch
+        {
+            ProtocolStatusCode.SessionNotFound or ProtocolStatusCode.SessionNotReady
+                => new MxGatewaySessionException(
+                    message,
+                    reply.SessionId,
+                    reply.CorrelationId,
+                    reply.ProtocolStatus,
+                    hResult,
+                    statuses),
+            ProtocolStatusCode.WorkerUnavailable
+                => new MxGatewayWorkerException(
+                    message,
+                    reply.SessionId,
+                    reply.CorrelationId,
+                    reply.ProtocolStatus,
+                    hResult,
+                    statuses),
+            _
+                => new MxGatewayCommandException(
+                    message,
+                    reply.SessionId,
+                    reply.CorrelationId,
+                    reply.ProtocolStatus,
+                    hResult,
+                    statuses),
+        };
+    }
+
+    private static string CreateProtocolMessage(MxCommandReply reply)
+    {
+        string statusMessage = string.IsNullOrWhiteSpace(reply.ProtocolStatus?.Message)
+            ? "Gateway protocol failure."
+            : reply.ProtocolStatus.Message;
+
+        return $"{statusMessage} code={reply.ProtocolStatus?.Code}; session={reply.SessionId}; correlation={reply.CorrelationId}";
+    }
+
+    private static string CreateMxAccessMessage(MxCommandReply reply)
+    {
+        string statusSummary = reply.Statuses.Count is 0
+            ? "no MXSTATUS_PROXY entries"
+            : string.Join("; ", reply.Statuses.Select(status => status.ToDiagnosticSummary()));
+
+        string hResult = reply.HasHresult
+            ? $"0x{reply.Hresult:X8}"
+            : "none";
+
+        return $"MXAccess command failed. kind={reply.Kind}; hresult={hResult}; statuses={statusSummary}";
+    }
+}
diff --git a/clients/dotnet/MxGateway.Client/MxGatewayAuthenticationException.cs b/clients/dotnet/MxGateway.Client/MxGatewayAuthenticationException.cs
new file mode 100644
index 0000000..e1164fb
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client/MxGatewayAuthenticationException.cs
@@ -0,0 +1,25 @@
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client;
+
+public sealed class MxGatewayAuthenticationException : MxGatewayException
+{
+    public MxGatewayAuthenticationException(
+        string message,
+        string? sessionId = null,
+        string? correlationId = null,
+        ProtocolStatus? protocolStatus = null,
+        int? hResult = null,
+        IReadOnlyList<MxStatusProxy>? statuses = null,
+        Exception? innerException = null)
+        : base(
+            message,
+            sessionId,
+            correlationId,
+            protocolStatus,
+            hResult,
+            statuses ?? [],
+            innerException)
+    {
+    }
+}
diff --git a/clients/dotnet/MxGateway.Client/MxGatewayAuthorizationException.cs b/clients/dotnet/MxGateway.Client/MxGatewayAuthorizationException.cs
new file mode 100644
index 0000000..1c1c67c
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client/MxGatewayAuthorizationException.cs
@@ -0,0 +1,25 @@
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client;
+
+public sealed class MxGatewayAuthorizationException : MxGatewayException
+{
+    public MxGatewayAuthorizationException(
+        string message,
+        string? sessionId = null,
+        string? correlationId = null,
+        ProtocolStatus? protocolStatus = null,
+        int? hResult = null,
+        IReadOnlyList<MxStatusProxy>? statuses = null,
+        Exception? innerException = null)
+        : base(
+            message,
+            sessionId,
+            correlationId,
+            protocolStatus,
+            hResult,
+            statuses ?? [],
+            innerException)
+    {
+    }
+}
diff --git a/clients/dotnet/MxGateway.Client/MxGatewayCommandException.cs b/clients/dotnet/MxGateway.Client/MxGatewayCommandException.cs
new file mode 100644
index 0000000..83baf90
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client/MxGatewayCommandException.cs
@@ -0,0 +1,25 @@
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client;
+
+public class MxGatewayCommandException : MxGatewayException
+{
+    public MxGatewayCommandException(
+        string message,
+        string? sessionId = null,
+        string? correlationId = null,
+        ProtocolStatus? protocolStatus = null,
+        int? hResult = null,
+        IReadOnlyList<MxStatusProxy>? statuses = null,
+        Exception? innerException = null)
+        : base(
+            message,
+            sessionId,
+            correlationId,
+            protocolStatus,
+            hResult,
+            statuses ?? [],
+            innerException)
+    {
+    }
+}
diff --git a/clients/dotnet/MxGateway.Client/MxGatewayException.cs b/clients/dotnet/MxGateway.Client/MxGatewayException.cs
new file mode 100644
index 0000000..eb5b59e
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client/MxGatewayException.cs
@@ -0,0 +1,45 @@
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client;
+
+public class MxGatewayException : Exception
+{
+    public MxGatewayException(string message)
+        : base(message)
+    {
+        Statuses = [];
+    }
+
+    public MxGatewayException(string message, Exception? innerException)
+        : base(message, innerException)
+    {
+        Statuses = [];
+    }
+
+    public MxGatewayException(
+        string message,
+        string? sessionId,
+        string? correlationId,
+        ProtocolStatus? protocolStatus,
+        int? hResult,
+        IReadOnlyList<MxStatusProxy> statuses,
+        Exception? innerException = null)
+        : base(message, innerException)
+    {
+        SessionId = sessionId;
+        CorrelationId = correlationId;
+        ProtocolStatus = protocolStatus;
+        HResultCode = hResult;
+        Statuses = statuses;
+    }
+
+    public string? SessionId { get; }
+
+    public string? CorrelationId { get; }
+
+    public ProtocolStatus? ProtocolStatus { get; }
+
+    public int? HResultCode { get; }
+
+    public IReadOnlyList<MxStatusProxy> Statuses { get; }
+}
diff --git a/clients/dotnet/MxGateway.Client/MxGatewaySession.cs b/clients/dotnet/MxGateway.Client/MxGatewaySession.cs
index 2081593..6dcaa38 100644
--- a/clients/dotnet/MxGateway.Client/MxGatewaySession.cs
+++ b/clients/dotnet/MxGateway.Client/MxGatewaySession.cs
@@ -56,6 +56,7 @@ public sealed class MxGatewaySession : IAsyncDisposable
     {
         MxCommandReply reply = await RegisterRawAsync(clientName, cancellationToken)
             .ConfigureAwait(false);
+        reply.EnsureProtocolSuccess().EnsureMxAccessSuccess();
         return reply.Register?.ServerHandle ?? reply.ReturnValue.Int32Value;
     }
 
@@ -84,6 +85,7 @@ public sealed class MxGatewaySession : IAsyncDisposable
                 itemDefinition,
                 cancellationToken)
             .ConfigureAwait(false);
+        reply.EnsureProtocolSuccess().EnsureMxAccessSuccess();
         return reply.AddItem?.ItemHandle ?? reply.ReturnValue.Int32Value;
     }
 
@@ -119,6 +121,7 @@ public sealed class MxGatewaySession : IAsyncDisposable
                 itemContext,
                 cancellationToken)
             .ConfigureAwait(false);
+        reply.EnsureProtocolSuccess().EnsureMxAccessSuccess();
         return reply.AddItem2?.ItemHandle ?? reply.ReturnValue.Int32Value;
     }
 
@@ -149,8 +152,9 @@ public sealed class MxGatewaySession : IAsyncDisposable
         int itemHandle,
         CancellationToken cancellationToken = default)
     {
-        await AdviseRawAsync(serverHandle, itemHandle, cancellationToken)
+        MxCommandReply reply = await AdviseRawAsync(serverHandle, itemHandle, cancellationToken)
             .ConfigureAwait(false);
+        reply.EnsureProtocolSuccess().EnsureMxAccessSuccess();
     }
 
     public Task<MxCommandReply> AdviseRawAsync(
@@ -178,8 +182,9 @@ public sealed class MxGatewaySession : IAsyncDisposable
         int userId,
         CancellationToken cancellationToken = default)
     {
-        await WriteRawAsync(serverHandle, itemHandle, value, userId, cancellationToken)
+        MxCommandReply reply = await WriteRawAsync(serverHandle, itemHandle, value, userId, cancellationToken)
             .ConfigureAwait(false);
+        reply.EnsureProtocolSuccess().EnsureMxAccessSuccess();
     }
 
     public Task<MxCommandReply> WriteRawAsync(
@@ -206,6 +211,52 @@ public sealed class MxGatewaySession : IAsyncDisposable
             cancellationToken);
     }
 
+    public async Task Write2Async(
+        int serverHandle,
+        int itemHandle,
+        MxValue value,
+        MxValue timestampValue,
+        int userId,
+        CancellationToken cancellationToken = default)
+    {
+        MxCommandReply reply = await Write2RawAsync(
+                serverHandle,
+                itemHandle,
+                value,
+                timestampValue,
+                userId,
+                cancellationToken)
+            .ConfigureAwait(false);
+        reply.EnsureProtocolSuccess().EnsureMxAccessSuccess();
+    }
+
+    public Task<MxCommandReply> Write2RawAsync(
+        int serverHandle,
+        int itemHandle,
+        MxValue value,
+        MxValue timestampValue,
+        int userId,
+        CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(value);
+        ArgumentNullException.ThrowIfNull(timestampValue);
+
+        return InvokeCommandAsync(
+            new MxCommand
+            {
+                Kind = MxCommandKind.Write2,
+                Write2 = new Write2Command
+                {
+                    ServerHandle = serverHandle,
+                    ItemHandle = itemHandle,
+                    Value = value,
+                    TimestampValue = timestampValue,
+                    UserId = userId,
+                },
+            },
+            cancellationToken);
+    }
+
     public Task<MxCommandReply> InvokeAsync(
         MxCommandRequest request,
         CancellationToken cancellationToken = default)
diff --git a/clients/dotnet/MxGateway.Client/MxGatewaySessionException.cs b/clients/dotnet/MxGateway.Client/MxGatewaySessionException.cs
new file mode 100644
index 0000000..f7ae5db
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client/MxGatewaySessionException.cs
@@ -0,0 +1,25 @@
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client;
+
+public sealed class MxGatewaySessionException : MxGatewayException
+{
+    public MxGatewaySessionException(
+        string message,
+        string? sessionId = null,
+        string? correlationId = null,
+        ProtocolStatus? protocolStatus = null,
+        int? hResult = null,
+        IReadOnlyList<MxStatusProxy>? statuses = null,
+        Exception? innerException = null)
+        : base(
+            message,
+            sessionId,
+            correlationId,
+            protocolStatus,
+            hResult,
+            statuses ?? [],
+            innerException)
+    {
+    }
+}
diff --git a/clients/dotnet/MxGateway.Client/MxGatewayWorkerException.cs b/clients/dotnet/MxGateway.Client/MxGatewayWorkerException.cs
new file mode 100644
index 0000000..794a10b
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client/MxGatewayWorkerException.cs
@@ -0,0 +1,25 @@
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client;
+
+public sealed class MxGatewayWorkerException : MxGatewayException
+{
+    public MxGatewayWorkerException(
+        string message,
+        string? sessionId = null,
+        string? correlationId = null,
+        ProtocolStatus? protocolStatus = null,
+        int? hResult = null,
+        IReadOnlyList<MxStatusProxy>? statuses = null,
+        Exception? innerException = null)
+        : base(
+            message,
+            sessionId,
+            correlationId,
+            protocolStatus,
+            hResult,
+            statuses ?? [],
+            innerException)
+    {
+    }
+}
diff --git a/clients/dotnet/MxGateway.Client/MxStatusProxyExtensions.cs b/clients/dotnet/MxGateway.Client/MxStatusProxyExtensions.cs
new file mode 100644
index 0000000..a3086b8
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client/MxStatusProxyExtensions.cs
@@ -0,0 +1,25 @@
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client;
+
+public static class MxStatusProxyExtensions
+{
+    public static bool IsSuccess(this MxStatusProxy status)
+    {
+        ArgumentNullException.ThrowIfNull(status);
+
+        return status.Success != 0
+            && status.Category is MxStatusCategory.Ok;
+    }
+
+    public static string ToDiagnosticSummary(this MxStatusProxy status)
+    {
+        ArgumentNullException.ThrowIfNull(status);
+
+        string diagnosticText = string.IsNullOrWhiteSpace(status.DiagnosticText)
+            ? "no diagnostic text"
+            : status.DiagnosticText;
+
+        return $"{status.Category} by {status.DetectedBy}; detail={status.Detail}; {diagnosticText}";
+    }
+}
diff --git a/clients/dotnet/MxGateway.Client/MxValueExtensions.cs b/clients/dotnet/MxGateway.Client/MxValueExtensions.cs
new file mode 100644
index 0000000..5b75d2c
--- /dev/null
+++ b/clients/dotnet/MxGateway.Client/MxValueExtensions.cs
@@ -0,0 +1,284 @@
+using Google.Protobuf;
+using Google.Protobuf.WellKnownTypes;
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Client;
+
+/// <summary>
+/// Creates and projects gateway MXAccess values without hiding the raw
+/// protobuf value carried by command replies and events.
+/// </summary>
+public static class MxValueExtensions
+{
+    public static MxValue ToMxValue(this bool value)
+    {
+        return new MxValue
+        {
+            DataType = MxDataType.Boolean,
+            VariantType = "VT_BOOL",
+            BoolValue = value,
+        };
+    }
+
+    public static MxValue ToMxValue(this int value)
+    {
+        return new MxValue
+        {
+            DataType = MxDataType.Integer,
+            VariantType = "VT_I4",
+            Int32Value = value,
+        };
+    }
+
+    public static MxValue ToMxValue(this long value)
+    {
+        return new MxValue
+        {
+            DataType = MxDataType.Integer,
+            VariantType = "VT_I8",
+            Int64Value = value,
+        };
+    }
+
+    public static MxValue ToMxValue(this float value)
+    {
+        return new MxValue
+        {
+            DataType = MxDataType.Float,
+            VariantType = "VT_R4",
+            FloatValue = value,
+        };
+    }
+
+    public static MxValue ToMxValue(this double value)
+    {
+        return new MxValue
+        {
+            DataType = MxDataType.Double,
+            VariantType = "VT_R8",
+            DoubleValue = value,
+        };
+    }
+
+    public static MxValue ToMxValue(this string value)
+    {
+        ArgumentNullException.ThrowIfNull(value);
+
+        return new MxValue
+        {
+            DataType = MxDataType.String,
+            VariantType = "VT_BSTR",
+            StringValue = value,
+        };
+    }
+
+    public static MxValue ToMxValue(this DateTimeOffset value)
+    {
+        return new MxValue
+        {
+            DataType = MxDataType.Time,
+            VariantType = "VT_DATE",
+            TimestampValue = Timestamp.FromDateTimeOffset(value),
+        };
+    }
+
+    public static MxValue ToMxValue(this DateTime value)
+    {
+        return new DateTimeOffset(
+                value.Kind == DateTimeKind.Unspecified
+                    ? DateTime.SpecifyKind(value, DateTimeKind.Utc)
+                    : value.ToUniversalTime())
+            .ToMxValue();
+    }
+
+    public static MxValue ToMxValue(this IReadOnlyList<bool> values)
+    {
+        ArgumentNullException.ThrowIfNull(values);
+
+        var array = new BoolArray();
+        array.Values.Add(values);
+        return CreateArrayValue(MxDataType.Boolean, "VT_ARRAY|VT_BOOL", values.Count, new MxArray
+        {
+            ElementDataType = MxDataType.Boolean,
+            VariantType = "VT_ARRAY|VT_BOOL",
+            BoolValues = array,
+        });
+    }
+
+    public static MxValue ToMxValue(this IReadOnlyList<int> values)
+    {
+        ArgumentNullException.ThrowIfNull(values);
+
+        var array = new Int32Array();
+        array.Values.Add(values);
+        return CreateArrayValue(MxDataType.Integer, "VT_ARRAY|VT_I4", values.Count, new MxArray
+        {
+            ElementDataType = MxDataType.Integer,
+            VariantType = "VT_ARRAY|VT_I4",
+            Int32Values = array,
+        });
+    }
+
+    public static MxValue ToMxValue(this IReadOnlyList<long> values)
+    {
+        ArgumentNullException.ThrowIfNull(values);
+
+        var array = new Int64Array();
+        array.Values.Add(values);
+        return CreateArrayValue(MxDataType.Integer, "VT_ARRAY|VT_I8", values.Count, new MxArray
+        {
+            ElementDataType = MxDataType.Integer,
+            VariantType = "VT_ARRAY|VT_I8",
+            Int64Values = array,
+        });
+    }
+
+    public static MxValue ToMxValue(this IReadOnlyList<float> values)
+    {
+        ArgumentNullException.ThrowIfNull(values);
+
+        var array = new FloatArray();
+        array.Values.Add(values);
+        return CreateArrayValue(MxDataType.Float, "VT_ARRAY|VT_R4", values.Count, new MxArray
+        {
+            ElementDataType = MxDataType.Float,
+            VariantType = "VT_ARRAY|VT_R4",
+            FloatValues = array,
+        });
+    }
+
+    public static MxValue ToMxValue(this IReadOnlyList<double> values)
+    {
+        ArgumentNullException.ThrowIfNull(values);
+
+        var array = new DoubleArray();
+        array.Values.Add(values);
+        return CreateArrayValue(MxDataType.Double, "VT_ARRAY|VT_R8", values.Count, new MxArray
+        {
+            ElementDataType = MxDataType.Double,
+            VariantType = "VT_ARRAY|VT_R8",
+            DoubleValues = array,
+        });
+    }
+
+    public static MxValue ToMxValue(this IReadOnlyList<string> values)
+    {
+        ArgumentNullException.ThrowIfNull(values);
+
+        var array = new StringArray();
+        array.Values.Add(values);
+        return CreateArrayValue(MxDataType.String, "VT_ARRAY|VT_BSTR", values.Count, new MxArray
+        {
+            ElementDataType = MxDataType.String,
+            VariantType = "VT_ARRAY|VT_BSTR",
+            StringValues = array,
+        });
+    }
+
+    public static MxValue ToMxValue(this IReadOnlyList<DateTimeOffset> values)
+    {
+        ArgumentNullException.ThrowIfNull(values);
+
+        var array = new TimestampArray();
+        array.Values.Add(values.Select(Timestamp.FromDateTimeOffset));
+        return CreateArrayValue(MxDataType.Time, "VT_ARRAY|VT_DATE", values.Count, new MxArray
+        {
+            ElementDataType = MxDataType.Time,
+            VariantType = "VT_ARRAY|VT_DATE",
+            TimestampValues = array,
+        });
+    }
+
+    public static string GetProjectionKind(this MxValue value)
+    {
+        ArgumentNullException.ThrowIfNull(value);
+
+        return value.KindCase switch
+        {
+            MxValue.KindOneofCase.BoolValue => "boolValue",
+            MxValue.KindOneofCase.Int32Value => "int32Value",
+            MxValue.KindOneofCase.Int64Value => "int64Value",
+            MxValue.KindOneofCase.FloatValue => "floatValue",
+            MxValue.KindOneofCase.DoubleValue => "doubleValue",
+            MxValue.KindOneofCase.StringValue => "stringValue",
+            MxValue.KindOneofCase.TimestampValue => "timestampValue",
+            MxValue.KindOneofCase.ArrayValue => "arrayValue",
+            MxValue.KindOneofCase.RawValue => "rawValue",
+            _ => value.IsNull ? "nullValue" : "unspecified",
+        };
+    }
+
+    public static object? ToClrValue(this MxValue value)
+    {
+        ArgumentNullException.ThrowIfNull(value);
+
+        return value.KindCase switch
+        {
+            MxValue.KindOneofCase.BoolValue => value.BoolValue,
+            MxValue.KindOneofCase.Int32Value => value.Int32Value,
+            MxValue.KindOneofCase.Int64Value => value.Int64Value,
+            MxValue.KindOneofCase.FloatValue => value.FloatValue,
+            MxValue.KindOneofCase.DoubleValue => value.DoubleValue,
+            MxValue.KindOneofCase.StringValue => value.StringValue,
+            MxValue.KindOneofCase.TimestampValue => value.TimestampValue.ToDateTimeOffset(),
+            MxValue.KindOneofCase.ArrayValue => value.ArrayValue.ToClrArrayValue(),
+            MxValue.KindOneofCase.RawValue => value.RawValue.ToByteArray(),
+            _ => value.IsNull ? null : value,
+        };
+    }
+
+    public static object? ToClrArrayValue(this MxArray array)
+    {
+        ArgumentNullException.ThrowIfNull(array);
+
+        return array.ValuesCase switch
+        {
+            MxArray.ValuesOneofCase.BoolValues => array.BoolValues.Values.ToArray(),
+            MxArray.ValuesOneofCase.Int32Values => array.Int32Values.Values.ToArray(),
+            MxArray.ValuesOneofCase.Int64Values => array.Int64Values.Values.ToArray(),
+            MxArray.ValuesOneofCase.FloatValues => array.FloatValues.Values.ToArray(),
+            MxArray.ValuesOneofCase.DoubleValues => array.DoubleValues.Values.ToArray(),
+            MxArray.ValuesOneofCase.StringValues => array.StringValues.Values.ToArray(),
+            MxArray.ValuesOneofCase.TimestampValues => array.TimestampValues.Values
+                .Select(timestamp => timestamp.ToDateTimeOffset())
+                .ToArray(),
+            MxArray.ValuesOneofCase.RawValues => array.RawValues.Values
+                .Select(value => value.ToByteArray())
+                .ToArray(),
+            _ => null,
+        };
+    }
+
+    public static MxValue ToRawMxValue(
+        byte[] value,
+        string variantType,
+        string rawDiagnostic,
+        int rawDataType = 0)
+    {
+        ArgumentNullException.ThrowIfNull(value);
+
+        return new MxValue
+        {
+            DataType = MxDataType.Unknown,
+            VariantType = variantType,
+            RawDiagnostic = rawDiagnostic,
+            RawDataType = rawDataType,
+            RawValue = ByteString.CopyFrom(value),
+        };
+    }
+
+    private static MxValue CreateArrayValue(
+        MxDataType dataType,
+        string variantType,
+        int length,
+        MxArray array)
+    {
+        array.Dimensions.Add((uint)length);
+        return new MxValue
+        {
+            DataType = dataType,
+            VariantType = variantType,
+            ArrayValue = array,
+        };
+    }
+}
diff --git a/clients/dotnet/README.md b/clients/dotnet/README.md
index d77e0c6..89150da 100644
--- a/clients/dotnet/README.md
+++ b/clients/dotnet/README.md
@@ -63,3 +63,49 @@ complete `MxCommandReply`.
 
 `MxGatewaySession.CloseAsync` is explicit and idempotent. Repeated calls return
 the first `CloseSessionReply` instead of sending another close request.
+
+## Values, Status, And Errors
+
+The client provides extension helpers for generated protobuf values. Use
+`ToMxValue()` on .NET scalar values and typed arrays to create `MxValue`
+instances for `Write` and `Write2`. Use `ToClrValue()` and
+`GetProjectionKind()` when test or diagnostic code needs to inspect generated
+`MxValue` replies while preserving `rawDiagnostic`, raw data type fields, and
+raw byte payloads.
+
+`MxStatusProxy.IsSuccess()` and `ToDiagnosticSummary()` expose MXAccess status
+arrays without collapsing them into a single gateway success flag. Command
+reply helpers follow the same split:
+
+```csharp
+reply.EnsureProtocolSuccess();
+reply.EnsureMxAccessSuccess();
+```
+
+`EnsureProtocolSuccess()` raises gateway, session, worker, or command
+exceptions for gateway-level failures. It leaves
+`PROTOCOL_STATUS_CODE_MXACCESS_FAILURE` to `EnsureMxAccessSuccess()` so callers
+can keep the full `MxCommandReply`, HRESULT, and status array when MXAccess
+itself rejects a command. `MxAccessException.Reply` contains the raw generated
+reply.
+
+## CLI Usage
+
+The test CLI supports deterministic JSON output for automation:
+
+```powershell
+dotnet run --project clients/dotnet/MxGateway.Client.Cli -- version --json
+dotnet run --project clients/dotnet/MxGateway.Client.Cli -- open-session --endpoint http://localhost:5000 --api-key-env MXGATEWAY_API_KEY --json
+dotnet run --project clients/dotnet/MxGateway.Client.Cli -- register --session-id <id> --client-name mxgw-dotnet-cli --json
+dotnet run --project clients/dotnet/MxGateway.Client.Cli -- add-item --session-id <id> --server-handle 1 --item Area001.Pump001.Speed --json
+dotnet run --project clients/dotnet/MxGateway.Client.Cli -- advise --session-id <id> --server-handle 1 --item-handle 1 --json
+dotnet run --project clients/dotnet/MxGateway.Client.Cli -- write --session-id <id> --server-handle 1 --item-handle 1 --type int32 --value 123 --json
+dotnet run --project clients/dotnet/MxGateway.Client.Cli -- write2 --session-id <id> --server-handle 1 --item-handle 1 --type int32 --value 123 --timestamp 2026-01-01T00:00:00Z --json
+dotnet run --project clients/dotnet/MxGateway.Client.Cli -- stream-events --session-id <id> --max-events 1 --json
+dotnet run --project clients/dotnet/MxGateway.Client.Cli -- smoke --endpoint http://localhost:5000 --api-key-env MXGATEWAY_API_KEY --item Area001.Pump001.Speed --json
+```
+
+`smoke` opens a session, registers a client, adds one item, advises it,
+optionally writes a value when `--type` and `--value` are supplied, reads a
+bounded event stream, and closes the session in a `finally` block. CLI error
+output redacts API keys supplied through `--api-key`.