diff --git a/server/src/models.rs b/server/src/models.rs
new file mode 100644
index 0000000..95705c0
--- /dev/null
+++ b/server/src/models.rs
@@ -0,0 +1,145 @@
+use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
+use chrono::{DateTime, Utc};
+
+/// Status of a remote desktop session.
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+#[serde(rename_all = "lowercase")]
+pub enum SessionStatus {
+    /// Session created, waiting for an agent to connect.
+    Waiting,
+    /// Agent is streaming display/audio.
+    Active,
+    /// Session ended or agent disconnected.
+    Disconnected,
+}
+
+impl std::fmt::Display for SessionStatus {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            SessionStatus::Waiting => write!(f, "waiting"),
+            SessionStatus::Active => write!(f, "active"),
+            SessionStatus::Disconnected => write!(f, "disconnected"),
+        }
+    }
+}
+
+/// A remote desktop session. Each session corresponds to one VM / remote machine.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Session {
+    pub id: String,
+    pub status: SessionStatus,
+    pub created_at: DateTime<Utc>,
+    pub display_active: bool,
+    pub audio_active: bool,
+    /// Resolution reported by the agent (e.g. "1920x1080").
+    pub resolution: Option<String>,
+    /// Arbitrary key-value metadata attached to this session.
+    pub metadata: HashMap<String, String>,
+}
+
+impl Session {
+    pub fn new(id: String) -> Self {
+        Self {
+            id,
+            status: SessionStatus::Waiting,
+            created_at: Utc::now(),
+            display_active: false,
+            audio_active: false,
+            resolution: None,
+            metadata: HashMap::new(),
+        }
+    }
+}
+
+/// Connection metadata for a registered desktop agent.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AgentConnection {
+    pub agent_id: String,
+    pub session_id: String,
+    pub connected_at: DateTime<Utc>,
+    pub ip_address: String,
+    pub display_active: bool,
+    pub audio_active: bool,
+}
+
+/// Client type for WebSocket connections.
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+#[serde(rename_all = "lowercase")]
+pub enum ClientType {
+    /// Browser-based viewer watching the remote desktop.
+    Viewer,
+    /// Native agent executable running inside the VM.
+    Agent,
+}
+
+// ── WebSocket message types ──────────────────────────────────────────────────
+
+/// Every WebSocket frame carries a JSON envelope with a `msg_type` discriminator.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "msg_type", rename_all = "snake_case")]
+pub enum WsMessage {
+    // ── Agent → Server ───────────────────────────────────────────────────────
+    /// A single display frame, base64-encoded JPEG or PNG.
+    DisplayFrame { session_id: String, data: String, timestamp: Option<f64> },
+    /// An audio chunk, base64-encoded PCM / Opus / AAC.
+    AudioFrame { session_id: String, data: String, timestamp: Option<f64> },
+    /// Agent announces its capabilities and info on connect.
+    AgentInfo { session_id: String, agent_id: String, resolution: Option<String> },
+    /// Keep-alive ping from agent.
+    Heartbeat,
+
+    // ── Viewer → Server ──────────────────────────────────────────────────────
+    /// Viewer sends a HUD (heads-up display) command to the agent.
+    HudCommand { session_id: String, command: String, params: serde_json::Value },
+    /// Viewer requests display resize.
+    Resize { session_id: String, width: u32, height: u32 },
+
+    // ── Server → Viewer ──────────────────────────────────────────────────────
+    /// Server relays a display frame to viewers.
+    FrameBroadcast { data: String, content_type: String },
+    /// Server relays an audio chunk to viewers.
+    AudioBroadcast { data: String, content_type: String },
+    /// Session state update pushed to viewers.
+    SessionUpdate { session_id: String, status: SessionStatus, resolution: Option<String> },
+
+    // ── Server → Agent ───────────────────────────────────────────────────────
+    /// Server forwards a HUD command from a viewer to the agent.
+    ForwardHudCommand { command: String, params: serde_json::Value },
+    /// Server forwards a resize request from a viewer.
+    ForwardResize { width: u32, height: u32 },
+    /// Server tells the agent to start / stop streaming.
+    StreamControl { action: String },
+
+    // ── Generic ──────────────────────────────────────────────────────────────
+    Error { message: String },
+    Ack { message: String },
+}
+
+/// Response body for health-check and generic API responses.
+#[derive(Debug, Serialize)]
+pub struct ApiResponse<T: Serialize> {
+    pub ok: bool,
+    pub data: Option<T>,
+    pub error: Option<String>,
+}
+
+impl<T: Serialize> ApiResponse<T> {
+    pub fn ok(data: T) -> Self {
+        Self { ok: true, data: Some(data), error: None }
+    }
+
+    pub fn err(msg: impl Into<String>) -> Self {
+        Self { ok: false, data: None, error: Some(msg.into()) }
+    }
+}
+
+/// Health-check payload.
+#[derive(Debug, Serialize)]
+pub struct HealthInfo {
+    pub status: String,
+    pub uptime_secs: u64,
+    pub active_sessions: usize,
+    pub connected_agents: usize,
+    pub version: String,
+}