diff --git a/src/NATS.Server/Monitoring/Connz.cs b/src/NATS.Server/Monitoring/Connz.cs
new file mode 100644
index 0000000..d2a6f49
--- /dev/null
+++ b/src/NATS.Server/Monitoring/Connz.cs
@@ -0,0 +1,207 @@
+using System.Text.Json.Serialization;
+
+namespace NATS.Server.Monitoring;
+
+/// <summary>
+/// Connection information response. Corresponds to Go server/monitor.go Connz struct.
+/// </summary>
+public sealed class Connz
+{
+    [JsonPropertyName("server_id")]
+    public string Id { get; set; } = "";
+
+    [JsonPropertyName("now")]
+    public DateTime Now { get; set; }
+
+    [JsonPropertyName("num_connections")]
+    public int NumConns { get; set; }
+
+    [JsonPropertyName("total")]
+    public int Total { get; set; }
+
+    [JsonPropertyName("offset")]
+    public int Offset { get; set; }
+
+    [JsonPropertyName("limit")]
+    public int Limit { get; set; }
+
+    [JsonPropertyName("connections")]
+    public ConnInfo[] Conns { get; set; } = [];
+}
+
+/// <summary>
+/// Detailed information on a per-connection basis.
+/// Corresponds to Go server/monitor.go ConnInfo struct.
+/// </summary>
+public sealed class ConnInfo
+{
+    [JsonPropertyName("cid")]
+    public ulong Cid { get; set; }
+
+    [JsonPropertyName("kind")]
+    public string Kind { get; set; } = "";
+
+    [JsonPropertyName("type")]
+    public string Type { get; set; } = "";
+
+    [JsonPropertyName("ip")]
+    public string Ip { get; set; } = "";
+
+    [JsonPropertyName("port")]
+    public int Port { get; set; }
+
+    [JsonPropertyName("start")]
+    public DateTime Start { get; set; }
+
+    [JsonPropertyName("last_activity")]
+    public DateTime LastActivity { get; set; }
+
+    [JsonPropertyName("stop")]
+    public DateTime? Stop { get; set; }
+
+    [JsonPropertyName("reason")]
+    public string Reason { get; set; } = "";
+
+    [JsonPropertyName("rtt")]
+    public string Rtt { get; set; } = "";
+
+    [JsonPropertyName("uptime")]
+    public string Uptime { get; set; } = "";
+
+    [JsonPropertyName("idle")]
+    public string Idle { get; set; } = "";
+
+    [JsonPropertyName("pending_bytes")]
+    public int Pending { get; set; }
+
+    [JsonPropertyName("in_msgs")]
+    public long InMsgs { get; set; }
+
+    [JsonPropertyName("out_msgs")]
+    public long OutMsgs { get; set; }
+
+    [JsonPropertyName("in_bytes")]
+    public long InBytes { get; set; }
+
+    [JsonPropertyName("out_bytes")]
+    public long OutBytes { get; set; }
+
+    [JsonPropertyName("subscriptions")]
+    public uint NumSubs { get; set; }
+
+    [JsonPropertyName("subscriptions_list")]
+    public string[] Subs { get; set; } = [];
+
+    [JsonPropertyName("subscriptions_list_detail")]
+    public SubDetail[] SubsDetail { get; set; } = [];
+
+    [JsonPropertyName("name")]
+    public string Name { get; set; } = "";
+
+    [JsonPropertyName("lang")]
+    public string Lang { get; set; } = "";
+
+    [JsonPropertyName("version")]
+    public string Version { get; set; } = "";
+
+    [JsonPropertyName("authorized_user")]
+    public string AuthorizedUser { get; set; } = "";
+
+    [JsonPropertyName("account")]
+    public string Account { get; set; } = "";
+
+    [JsonPropertyName("tls_version")]
+    public string TlsVersion { get; set; } = "";
+
+    [JsonPropertyName("tls_cipher_suite")]
+    public string TlsCipherSuite { get; set; } = "";
+
+    [JsonPropertyName("tls_first")]
+    public bool TlsFirst { get; set; }
+
+    [JsonPropertyName("mqtt_client")]
+    public string MqttClient { get; set; } = "";
+}
+
+/// <summary>
+/// Subscription detail information.
+/// Corresponds to Go server/monitor.go SubDetail struct.
+/// </summary>
+public sealed class SubDetail
+{
+    [JsonPropertyName("account")]
+    public string Account { get; set; } = "";
+
+    [JsonPropertyName("subject")]
+    public string Subject { get; set; } = "";
+
+    [JsonPropertyName("qgroup")]
+    public string Queue { get; set; } = "";
+
+    [JsonPropertyName("sid")]
+    public string Sid { get; set; } = "";
+
+    [JsonPropertyName("msgs")]
+    public long Msgs { get; set; }
+
+    [JsonPropertyName("max")]
+    public long Max { get; set; }
+
+    [JsonPropertyName("cid")]
+    public ulong Cid { get; set; }
+}
+
+/// <summary>
+/// Sort options for connection listing.
+/// Corresponds to Go server/monitor_sort_opts.go SortOpt type.
+/// </summary>
+public enum SortOpt
+{
+    ByCid,
+    ByStart,
+    BySubs,
+    ByPending,
+    ByMsgsTo,
+    ByMsgsFrom,
+    ByBytesTo,
+    ByBytesFrom,
+    ByLast,
+    ByIdle,
+    ByUptime,
+}
+
+/// <summary>
+/// Connection state filter.
+/// Corresponds to Go server/monitor.go ConnState type.
+/// </summary>
+public enum ConnState
+{
+    Open,
+    Closed,
+    All,
+}
+
+/// <summary>
+/// Options passed to Connz() for filtering and sorting.
+/// Corresponds to Go server/monitor.go ConnzOptions struct.
+/// </summary>
+public sealed class ConnzOptions
+{
+    public SortOpt Sort { get; set; } = SortOpt.ByCid;
+
+    public bool Subscriptions { get; set; }
+
+    public bool SubscriptionsDetail { get; set; }
+
+    public ConnState State { get; set; } = ConnState.Open;
+
+    public string User { get; set; } = "";
+
+    public string Account { get; set; } = "";
+
+    public string FilterSubject { get; set; } = "";
+
+    public int Offset { get; set; }
+
+    public int Limit { get; set; } = 1024;
+}
diff --git a/src/NATS.Server/Monitoring/Varz.cs b/src/NATS.Server/Monitoring/Varz.cs
new file mode 100644
index 0000000..847bdc2
--- /dev/null
+++ b/src/NATS.Server/Monitoring/Varz.cs
@@ -0,0 +1,415 @@
+using System.Text.Json.Serialization;
+
+namespace NATS.Server.Monitoring;
+
+/// <summary>
+/// Server general information. Corresponds to Go server/monitor.go Varz struct.
+/// </summary>
+public sealed class Varz
+{
+    // Identity
+    [JsonPropertyName("server_id")]
+    public string Id { get; set; } = "";
+
+    [JsonPropertyName("server_name")]
+    public string Name { get; set; } = "";
+
+    [JsonPropertyName("version")]
+    public string Version { get; set; } = "";
+
+    [JsonPropertyName("proto")]
+    public int Proto { get; set; }
+
+    [JsonPropertyName("git_commit")]
+    public string GitCommit { get; set; } = "";
+
+    [JsonPropertyName("go")]
+    public string GoVersion { get; set; } = "";
+
+    [JsonPropertyName("host")]
+    public string Host { get; set; } = "";
+
+    [JsonPropertyName("port")]
+    public int Port { get; set; }
+
+    // Network
+    [JsonPropertyName("ip")]
+    public string Ip { get; set; } = "";
+
+    [JsonPropertyName("connect_urls")]
+    public string[] ConnectUrls { get; set; } = [];
+
+    [JsonPropertyName("ws_connect_urls")]
+    public string[] WsConnectUrls { get; set; } = [];
+
+    [JsonPropertyName("http_host")]
+    public string HttpHost { get; set; } = "";
+
+    [JsonPropertyName("http_port")]
+    public int HttpPort { get; set; }
+
+    [JsonPropertyName("http_base_path")]
+    public string HttpBasePath { get; set; } = "";
+
+    [JsonPropertyName("https_port")]
+    public int HttpsPort { get; set; }
+
+    // Security
+    [JsonPropertyName("auth_required")]
+    public bool AuthRequired { get; set; }
+
+    [JsonPropertyName("tls_required")]
+    public bool TlsRequired { get; set; }
+
+    [JsonPropertyName("tls_verify")]
+    public bool TlsVerify { get; set; }
+
+    [JsonPropertyName("tls_ocsp_peer_verify")]
+    public bool TlsOcspPeerVerify { get; set; }
+
+    [JsonPropertyName("auth_timeout")]
+    public double AuthTimeout { get; set; }
+
+    [JsonPropertyName("tls_timeout")]
+    public double TlsTimeout { get; set; }
+
+    // Limits
+    [JsonPropertyName("max_connections")]
+    public int MaxConnections { get; set; }
+
+    [JsonPropertyName("max_subscriptions")]
+    public int MaxSubscriptions { get; set; }
+
+    [JsonPropertyName("max_payload")]
+    public int MaxPayload { get; set; }
+
+    [JsonPropertyName("max_pending")]
+    public long MaxPending { get; set; }
+
+    [JsonPropertyName("max_control_line")]
+    public int MaxControlLine { get; set; }
+
+    [JsonPropertyName("ping_max")]
+    public int MaxPingsOut { get; set; }
+
+    // Timing
+    [JsonPropertyName("ping_interval")]
+    public long PingInterval { get; set; }
+
+    [JsonPropertyName("write_deadline")]
+    public long WriteDeadline { get; set; }
+
+    [JsonPropertyName("start")]
+    public DateTime Start { get; set; }
+
+    [JsonPropertyName("now")]
+    public DateTime Now { get; set; }
+
+    [JsonPropertyName("uptime")]
+    public string Uptime { get; set; } = "";
+
+    // Runtime
+    [JsonPropertyName("mem")]
+    public long Mem { get; set; }
+
+    [JsonPropertyName("cpu")]
+    public double Cpu { get; set; }
+
+    [JsonPropertyName("cores")]
+    public int Cores { get; set; }
+
+    [JsonPropertyName("gomaxprocs")]
+    public int MaxProcs { get; set; }
+
+    // Connections
+    [JsonPropertyName("connections")]
+    public int Connections { get; set; }
+
+    [JsonPropertyName("total_connections")]
+    public ulong TotalConnections { get; set; }
+
+    [JsonPropertyName("routes")]
+    public int Routes { get; set; }
+
+    [JsonPropertyName("remotes")]
+    public int Remotes { get; set; }
+
+    [JsonPropertyName("leafnodes")]
+    public int Leafnodes { get; set; }
+
+    // Messages
+    [JsonPropertyName("in_msgs")]
+    public long InMsgs { get; set; }
+
+    [JsonPropertyName("out_msgs")]
+    public long OutMsgs { get; set; }
+
+    [JsonPropertyName("in_bytes")]
+    public long InBytes { get; set; }
+
+    [JsonPropertyName("out_bytes")]
+    public long OutBytes { get; set; }
+
+    // Health
+    [JsonPropertyName("slow_consumers")]
+    public long SlowConsumers { get; set; }
+
+    [JsonPropertyName("slow_consumer_stats")]
+    public SlowConsumersStats SlowConsumerStats { get; set; } = new();
+
+    [JsonPropertyName("subscriptions")]
+    public uint Subscriptions { get; set; }
+
+    // Config
+    [JsonPropertyName("config_load_time")]
+    public DateTime ConfigLoadTime { get; set; }
+
+    [JsonPropertyName("tags")]
+    public string[] Tags { get; set; } = [];
+
+    [JsonPropertyName("system_account")]
+    public string SystemAccount { get; set; } = "";
+
+    [JsonPropertyName("pinned_account_fails")]
+    public ulong PinnedAccountFail { get; set; }
+
+    [JsonPropertyName("tls_cert_not_after")]
+    public DateTime TlsCertNotAfter { get; set; }
+
+    // HTTP
+    [JsonPropertyName("http_req_stats")]
+    public Dictionary<string, ulong> HttpReqStats { get; set; } = new();
+
+    // Subsystems
+    [JsonPropertyName("cluster")]
+    public ClusterOptsVarz Cluster { get; set; } = new();
+
+    [JsonPropertyName("gateway")]
+    public GatewayOptsVarz Gateway { get; set; } = new();
+
+    [JsonPropertyName("leaf")]
+    public LeafNodeOptsVarz Leaf { get; set; } = new();
+
+    [JsonPropertyName("mqtt")]
+    public MqttOptsVarz Mqtt { get; set; } = new();
+
+    [JsonPropertyName("websocket")]
+    public WebsocketOptsVarz Websocket { get; set; } = new();
+
+    [JsonPropertyName("jetstream")]
+    public JetStreamVarz JetStream { get; set; } = new();
+}
+
+/// <summary>
+/// Statistics about slow consumers by connection type.
+/// Corresponds to Go server/monitor.go SlowConsumersStats struct.
+/// </summary>
+public sealed class SlowConsumersStats
+{
+    [JsonPropertyName("clients")]
+    public ulong Clients { get; set; }
+
+    [JsonPropertyName("routes")]
+    public ulong Routes { get; set; }
+
+    [JsonPropertyName("gateways")]
+    public ulong Gateways { get; set; }
+
+    [JsonPropertyName("leafs")]
+    public ulong Leafs { get; set; }
+}
+
+/// <summary>
+/// Cluster configuration monitoring information.
+/// Corresponds to Go server/monitor.go ClusterOptsVarz struct.
+/// </summary>
+public sealed class ClusterOptsVarz
+{
+    [JsonPropertyName("name")]
+    public string Name { get; set; } = "";
+
+    [JsonPropertyName("addr")]
+    public string Host { get; set; } = "";
+
+    [JsonPropertyName("cluster_port")]
+    public int Port { get; set; }
+
+    [JsonPropertyName("auth_timeout")]
+    public double AuthTimeout { get; set; }
+
+    [JsonPropertyName("tls_timeout")]
+    public double TlsTimeout { get; set; }
+
+    [JsonPropertyName("tls_required")]
+    public bool TlsRequired { get; set; }
+
+    [JsonPropertyName("tls_verify")]
+    public bool TlsVerify { get; set; }
+
+    [JsonPropertyName("pool_size")]
+    public int PoolSize { get; set; }
+
+    [JsonPropertyName("urls")]
+    public string[] Urls { get; set; } = [];
+}
+
+/// <summary>
+/// Gateway configuration monitoring information.
+/// Corresponds to Go server/monitor.go GatewayOptsVarz struct.
+/// </summary>
+public sealed class GatewayOptsVarz
+{
+    [JsonPropertyName("name")]
+    public string Name { get; set; } = "";
+
+    [JsonPropertyName("host")]
+    public string Host { get; set; } = "";
+
+    [JsonPropertyName("port")]
+    public int Port { get; set; }
+
+    [JsonPropertyName("auth_timeout")]
+    public double AuthTimeout { get; set; }
+
+    [JsonPropertyName("tls_timeout")]
+    public double TlsTimeout { get; set; }
+
+    [JsonPropertyName("tls_required")]
+    public bool TlsRequired { get; set; }
+
+    [JsonPropertyName("tls_verify")]
+    public bool TlsVerify { get; set; }
+
+    [JsonPropertyName("advertise")]
+    public string Advertise { get; set; } = "";
+
+    [JsonPropertyName("connect_retries")]
+    public int ConnectRetries { get; set; }
+
+    [JsonPropertyName("reject_unknown")]
+    public bool RejectUnknown { get; set; }
+}
+
+/// <summary>
+/// Leaf node configuration monitoring information.
+/// Corresponds to Go server/monitor.go LeafNodeOptsVarz struct.
+/// </summary>
+public sealed class LeafNodeOptsVarz
+{
+    [JsonPropertyName("host")]
+    public string Host { get; set; } = "";
+
+    [JsonPropertyName("port")]
+    public int Port { get; set; }
+
+    [JsonPropertyName("auth_timeout")]
+    public double AuthTimeout { get; set; }
+
+    [JsonPropertyName("tls_timeout")]
+    public double TlsTimeout { get; set; }
+
+    [JsonPropertyName("tls_required")]
+    public bool TlsRequired { get; set; }
+
+    [JsonPropertyName("tls_verify")]
+    public bool TlsVerify { get; set; }
+
+    [JsonPropertyName("tls_ocsp_peer_verify")]
+    public bool TlsOcspPeerVerify { get; set; }
+}
+
+/// <summary>
+/// MQTT configuration monitoring information.
+/// Corresponds to Go server/monitor.go MQTTOptsVarz struct.
+/// </summary>
+public sealed class MqttOptsVarz
+{
+    [JsonPropertyName("host")]
+    public string Host { get; set; } = "";
+
+    [JsonPropertyName("port")]
+    public int Port { get; set; }
+
+    [JsonPropertyName("tls_timeout")]
+    public double TlsTimeout { get; set; }
+}
+
+/// <summary>
+/// Websocket configuration monitoring information.
+/// Corresponds to Go server/monitor.go WebsocketOptsVarz struct.
+/// </summary>
+public sealed class WebsocketOptsVarz
+{
+    [JsonPropertyName("host")]
+    public string Host { get; set; } = "";
+
+    [JsonPropertyName("port")]
+    public int Port { get; set; }
+
+    [JsonPropertyName("tls_timeout")]
+    public double TlsTimeout { get; set; }
+}
+
+/// <summary>
+/// JetStream runtime information.
+/// Corresponds to Go server/monitor.go JetStreamVarz struct.
+/// </summary>
+public sealed class JetStreamVarz
+{
+    [JsonPropertyName("config")]
+    public JetStreamConfig Config { get; set; } = new();
+
+    [JsonPropertyName("stats")]
+    public JetStreamStats Stats { get; set; } = new();
+}
+
+/// <summary>
+/// JetStream configuration.
+/// Corresponds to Go server/jetstream.go JetStreamConfig struct.
+/// </summary>
+public sealed class JetStreamConfig
+{
+    [JsonPropertyName("max_memory")]
+    public long MaxMemory { get; set; }
+
+    [JsonPropertyName("max_storage")]
+    public long MaxStorage { get; set; }
+
+    [JsonPropertyName("store_dir")]
+    public string StoreDir { get; set; } = "";
+}
+
+/// <summary>
+/// JetStream statistics.
+/// Corresponds to Go server/jetstream.go JetStreamStats struct.
+/// </summary>
+public sealed class JetStreamStats
+{
+    [JsonPropertyName("memory")]
+    public ulong Memory { get; set; }
+
+    [JsonPropertyName("storage")]
+    public ulong Storage { get; set; }
+
+    [JsonPropertyName("accounts")]
+    public int Accounts { get; set; }
+
+    [JsonPropertyName("ha_assets")]
+    public int HaAssets { get; set; }
+
+    [JsonPropertyName("api")]
+    public JetStreamApiStats Api { get; set; } = new();
+}
+
+/// <summary>
+/// JetStream API statistics.
+/// Corresponds to Go server/jetstream.go JetStreamAPIStats struct.
+/// </summary>
+public sealed class JetStreamApiStats
+{
+    [JsonPropertyName("total")]
+    public ulong Total { get; set; }
+
+    [JsonPropertyName("errors")]
+    public ulong Errors { get; set; }
+}
diff --git a/tests/NATS.Server.Tests/MonitorModelTests.cs b/tests/NATS.Server.Tests/MonitorModelTests.cs
new file mode 100644
index 0000000..690afd5
--- /dev/null
+++ b/tests/NATS.Server.Tests/MonitorModelTests.cs
@@ -0,0 +1,51 @@
+using System.Text.Json;
+using NATS.Server.Monitoring;
+
+namespace NATS.Server.Tests;
+
+public class MonitorModelTests
+{
+    [Fact]
+    public void Varz_serializes_with_go_field_names()
+    {
+        var varz = new Varz
+        {
+            Id = "TESTID", Name = "test-server", Version = "0.1.0",
+            Host = "0.0.0.0", Port = 4222, InMsgs = 100, OutMsgs = 200,
+        };
+        var json = JsonSerializer.Serialize(varz);
+        json.ShouldContain("\"server_id\":");
+        json.ShouldContain("\"server_name\":");
+        json.ShouldContain("\"in_msgs\":");
+        json.ShouldContain("\"out_msgs\":");
+        json.ShouldNotContain("\"InMsgs\"");
+    }
+
+    [Fact]
+    public void Connz_serializes_with_go_field_names()
+    {
+        var connz = new Connz
+        {
+            Id = "TESTID", Now = DateTime.UtcNow, NumConns = 1, Total = 1, Limit = 1024,
+            Conns = [new ConnInfo { Cid = 1, Ip = "127.0.0.1", Port = 5555,
+                InMsgs = 10, Uptime = "1s", Idle = "0s",
+                Start = DateTime.UtcNow, LastActivity = DateTime.UtcNow }],
+        };
+        var json = JsonSerializer.Serialize(connz);
+        json.ShouldContain("\"server_id\":");
+        json.ShouldContain("\"num_connections\":");
+        json.ShouldContain("\"in_msgs\":");
+        json.ShouldContain("\"pending_bytes\":");
+    }
+
+    [Fact]
+    public void Varz_includes_nested_config_stubs()
+    {
+        var varz = new Varz { Id = "X", Name = "X", Version = "X", Host = "X" };
+        var json = JsonSerializer.Serialize(varz);
+        json.ShouldContain("\"cluster\":");
+        json.ShouldContain("\"gateway\":");
+        json.ShouldContain("\"leaf\":");
+        json.ShouldContain("\"jetstream\":");
+    }
+}