diff --git a/Cargo.toml b/Cargo.toml
index 04e3f381..328359c2 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,6 +6,7 @@ members = [
     "mofa-dora-bridge",
     "mofa-ui",
     "apps/*",
+    "libs/mofa-metrics",
 ]
 exclude = ["apps/mofa-asr"]
 
diff --git a/libs/mofa-metrics/Cargo.toml b/libs/mofa-metrics/Cargo.toml
new file mode 100644
index 00000000..e8e2cad7
--- /dev/null
+++ b/libs/mofa-metrics/Cargo.toml
@@ -0,0 +1,20 @@
+[package]
+name = "mofa-metrics"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+description = "Thread-safe metrics store and HTTP/WebSocket API for MoFA Studio Observatory"
+
+[dependencies]
+serde = { workspace = true }
+serde_json = { workspace = true }
+parking_lot = { workspace = true }
+tokio = { workspace = true }
+log = { workspace = true }
+uuid = { workspace = true }
+axum = { version = "0.7", features = ["ws"] }
+tower-http = { version = "0.5", features = ["cors", "timeout"] }
+futures = "0.3"
+
+[dev-dependencies]
+tokio = { workspace = true, features = ["full", "macros", "rt-multi-thread"] }
diff --git a/libs/mofa-metrics/src/lib.rs b/libs/mofa-metrics/src/lib.rs
new file mode 100644
index 00000000..f7289c75
--- /dev/null
+++ b/libs/mofa-metrics/src/lib.rs
@@ -0,0 +1,9 @@
+// Metrics store and HTTP/WS API for MoFA Studio Observatory.
+
+pub mod server;
+pub mod store;
+pub mod types;
+
+pub use server::ServerConfig;
+pub use store::MetricsStore;
+pub use types::*;
diff --git a/libs/mofa-metrics/src/server.rs b/libs/mofa-metrics/src/server.rs
new file mode 100644
index 00000000..c77b494c
--- /dev/null
+++ b/libs/mofa-metrics/src/server.rs
@@ -0,0 +1,113 @@
+// HTTP + WebSocket server for Observatory metrics API.
+
+use axum::extract::ws::{Message, WebSocket, WebSocketUpgrade};
+use axum::extract::{Path, State};
+use axum::http::StatusCode;
+use axum::response::IntoResponse;
+use axum::routing::get;
+use axum::{Json, Router};
+use futures::{sink::SinkExt, stream::StreamExt};
+use std::net::SocketAddr;
+use std::sync::Arc;
+use std::time::Duration;
+use tokio::net::TcpListener;
+use tokio::sync::broadcast;
+use tower_http::cors::CorsLayer;
+use tower_http::timeout::TimeoutLayer;
+
+use crate::{AgentStatus, MetricsStore, PipelineTrace, SystemSnapshot};
+
+/// Server config.
+pub struct ServerConfig {
+    pub port: u16,
+}
+
+/// Start metrics server as a background task.
+pub fn start(store: Arc<MetricsStore>, cfg: ServerConfig) -> tokio::task::JoinHandle<()> {
+    tokio::spawn(async move {
+        let (tx, _) = broadcast::channel::<String>(256);
+        store.init_broadcast(tx);
+
+        let app = Router::new()
+            .route("/api/agents", get(h_list_agents))
+            .route("/api/agents/{id}", get(h_get_agent))
+            .route("/api/metrics", get(h_get_metrics))
+            .route("/api/pipeline", get(h_get_pipeline))
+            .route("/ws", get(h_ws))
+            .layer(CorsLayer::permissive())
+            .layer(TimeoutLayer::new(Duration::from_secs(30)))
+            .with_state(store);
+
+        let addr = SocketAddr::from(([0, 0, 0, 0], cfg.port));
+        let listener = match TcpListener::bind(addr).await {
+            Ok(l) => l,
+            Err(e) => {
+                log::error!("Failed to bind metrics server on port {}: {}", cfg.port, e);
+                return;
+            }
+        };
+        log::info!(
+            "Observatory HTTP server listening on http://localhost:{}",
+            cfg.port
+        );
+        axum::serve(listener, app).await.ok();
+    })
+}
+
+// REST handlers
+async fn h_list_agents(State(s): State<Arc<MetricsStore>>) -> Json<Vec<AgentStatus>> {
+    Json(s.get_agents())
+}
+
+async fn h_get_agent(
+    State(s): State<Arc<MetricsStore>>,
+    Path(id): Path<String>,
+) -> Result<Json<AgentStatus>, StatusCode> {
+    s.get_agents()
+        .into_iter()
+        .find(|a| a.id == id)
+        .map(Json)
+        .ok_or(StatusCode::NOT_FOUND)
+}
+
+async fn h_get_metrics(State(s): State<Arc<MetricsStore>>) -> Json<Option<SystemSnapshot>> {
+    Json(s.get_latest_snapshot())
+}
+
+async fn h_get_pipeline(State(s): State<Arc<MetricsStore>>) -> Json<Vec<PipelineTrace>> {
+    Json(s.get_traces(50))
+}
+
+// WebSocket
+async fn h_ws(ws: WebSocketUpgrade, State(s): State<Arc<MetricsStore>>) -> impl IntoResponse {
+    ws.on_upgrade(|socket| ws_handler(socket, s))
+}
+
+async fn ws_handler(socket: WebSocket, store: Arc<MetricsStore>) {
+    let Some(mut rx) = store.subscribe() else {
+        return;
+    };
+    let (mut sender, mut receiver): (
+        futures::stream::SplitSink<WebSocket, Message>,
+        futures::stream::SplitStream<WebSocket>,
+    ) = socket.split();
+
+    loop {
+        tokio::select! {
+            msg = rx.recv() => {
+                match msg {
+                    Ok(json) => {
+                        let text_msg: Message = Message::Text(json.into());
+                        if sender.send(text_msg).await.is_err() {
+                            break;
+                        }
+                    }
+                    Err(_) => break,
+                }
+            }
+            incoming = receiver.next() => {
+                if incoming.is_none() { break; }
+            }
+        }
+    }
+}
diff --git a/libs/mofa-metrics/src/store.rs b/libs/mofa-metrics/src/store.rs
new file mode 100644
index 00000000..90e75ce2
--- /dev/null
+++ b/libs/mofa-metrics/src/store.rs
@@ -0,0 +1,212 @@
+// Thread-safe metrics store with dirty tracking.
+
+use crate::{AgentStatus, MetricEvent, PipelineTrace, SystemSnapshot};
+use parking_lot::RwLock;
+use std::collections::{HashMap, VecDeque};
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::Arc;
+use tokio::sync::broadcast;
+
+pub struct MetricsStore {
+    agents: RwLock<HashMap<String, AgentStatus>>,
+    traces: RwLock<VecDeque<PipelineTrace>>,
+    snapshots: RwLock<VecDeque<SystemSnapshot>>,
+
+    agents_dirty: AtomicBool,
+    traces_dirty: AtomicBool,
+    snapshots_dirty: AtomicBool,
+
+    broadcast_tx: RwLock<Option<broadcast::Sender<String>>>,
+}
+
+// Ring buffer caps
+const MAX_TRACES: usize = 200;
+const MAX_SNAPSHOTS: usize = 300;
+
+impl MetricsStore {
+    pub fn new() -> Arc<Self> {
+        Arc::new(Self {
+            agents: RwLock::new(HashMap::new()),
+            traces: RwLock::new(VecDeque::new()),
+            snapshots: RwLock::new(VecDeque::new()),
+            agents_dirty: AtomicBool::new(false),
+            traces_dirty: AtomicBool::new(false),
+            snapshots_dirty: AtomicBool::new(false),
+            broadcast_tx: RwLock::new(None),
+        })
+    }
+
+    pub fn init_broadcast(&self, tx: broadcast::Sender<String>) {
+        *self.broadcast_tx.write() = Some(tx);
+    }
+
+    pub fn subscribe(&self) -> Option<broadcast::Receiver<String>> {
+        self.broadcast_tx.read().as_ref().map(|tx| tx.subscribe())
+    }
+
+    fn broadcast_event(&self, event: &MetricEvent) {
+        if let Some(ref tx) = *self.broadcast_tx.read() {
+            if let Ok(json) = serde_json::to_string(event) {
+                let _ = tx.send(json);
+            }
+        }
+    }
+
+    pub fn record_agent(&self, status: AgentStatus) {
+        self.broadcast_event(&MetricEvent::AgentStatusChanged(status.clone()));
+        self.agents.write().insert(status.id.clone(), status);
+        self.agents_dirty.store(true, Ordering::Release);
+    }
+
+    pub fn push_trace(&self, trace: PipelineTrace) {
+        self.broadcast_event(&MetricEvent::PipelineCompleted(trace.clone()));
+        let mut buf = self.traces.write();
+        if buf.len() >= MAX_TRACES {
+            buf.pop_front();
+        }
+        buf.push_back(trace);
+        self.traces_dirty.store(true, Ordering::Release);
+    }
+
+    pub fn push_snapshot(&self, snap: SystemSnapshot) {
+        self.broadcast_event(&MetricEvent::SystemSnapshot(snap.clone()));
+        let mut buf = self.snapshots.write();
+        if buf.len() >= MAX_SNAPSHOTS {
+            buf.pop_front();
+        }
+        buf.push_back(snap);
+        self.snapshots_dirty.store(true, Ordering::Release);
+    }
+
+    pub fn take_agents_if_dirty(&self) -> Option<Vec<AgentStatus>> {
+        if self.agents_dirty.swap(false, Ordering::AcqRel) {
+            Some(self.agents.read().values().cloned().collect())
+        } else {
+            None
+        }
+    }
+
+    pub fn take_traces_if_dirty(&self) -> Option<Vec<PipelineTrace>> {
+        if self.traces_dirty.swap(false, Ordering::AcqRel) {
+            Some(self.traces.read().iter().cloned().collect())
+        } else {
+            None
+        }
+    }
+
+    pub fn take_snapshots_if_dirty(&self) -> Option<Vec<SystemSnapshot>> {
+        if self.snapshots_dirty.swap(false, Ordering::AcqRel) {
+            Some(self.snapshots.read().iter().cloned().collect())
+        } else {
+            None
+        }
+    }
+
+    pub fn get_agents(&self) -> Vec<AgentStatus> {
+        self.agents.read().values().cloned().collect()
+    }
+
+    pub fn get_latest_snapshot(&self) -> Option<SystemSnapshot> {
+        self.snapshots.read().back().cloned()
+    }
+
+    pub fn get_traces(&self, n: usize) -> Vec<PipelineTrace> {
+        let buf = self.traces.read();
+        buf.iter().rev().take(n).rev().cloned().collect()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::types::{unix_ms, AgentState};
+
+    fn sample_agent(id: &str, state: AgentState) -> AgentStatus {
+        AgentStatus {
+            id: id.into(),
+            name: id.into(),
+            status: state,
+            last_seen_ms: unix_ms(),
+        }
+    }
+
+    fn sample_snapshot() -> SystemSnapshot {
+        SystemSnapshot {
+            cpu_pct: 0.45,
+            memory_pct: 0.60,
+            gpu_pct: 0.0,
+            pipeline_latency_p50_ms: 120.0,
+            uptime_secs: 30,
+            timestamp_ms: unix_ms(),
+        }
+    }
+
+    #[test]
+    fn dirty_flag_cleared_on_read() {
+        let store = MetricsStore::new();
+        assert!(store.take_agents_if_dirty().is_none());
+
+        store.record_agent(sample_agent("n1", AgentState::Active));
+        let agents = store.take_agents_if_dirty().unwrap();
+        assert_eq!(agents.len(), 1);
+
+        // Not dirty anymore
+        assert!(store.take_agents_if_dirty().is_none());
+    }
+
+    #[test]
+    fn agent_upsert() {
+        let store = MetricsStore::new();
+        store.record_agent(sample_agent("n1", AgentState::Idle));
+        store.record_agent(sample_agent("n1", AgentState::Active));
+
+        let agents = store.get_agents();
+        assert_eq!(agents.len(), 1);
+        assert_eq!(agents[0].status, AgentState::Active);
+    }
+
+    #[test]
+    fn trace_ring_buffer_cap() {
+        let store = MetricsStore::new();
+        for i in 0..(MAX_TRACES + 50) {
+            store.push_trace(PipelineTrace {
+                asr_start_ms: i as u64,
+                asr_end_ms: i as u64 + 10,
+                llm_start_ms: 0,
+                llm_end_ms: 0,
+                tts_start_ms: 0,
+                tts_end_ms: 0,
+                tokens_per_sec: 0.0,
+            });
+        }
+        let traces = store.get_traces(999);
+        assert_eq!(traces.len(), MAX_TRACES);
+        // Oldest evicted
+        assert_eq!(traces[0].asr_start_ms, 50);
+    }
+
+    #[test]
+    fn snapshot_ring_buffer_cap() {
+        let store = MetricsStore::new();
+        for _ in 0..(MAX_SNAPSHOTS + 10) {
+            store.push_snapshot(sample_snapshot());
+        }
+        let snaps = store.take_snapshots_if_dirty().unwrap();
+        assert_eq!(snaps.len(), MAX_SNAPSHOTS);
+    }
+
+    #[test]
+    fn get_latest_snapshot_returns_newest() {
+        let store = MetricsStore::new();
+        store.push_snapshot(SystemSnapshot {
+            cpu_pct: 0.1,
+            ..sample_snapshot()
+        });
+        store.push_snapshot(SystemSnapshot {
+            cpu_pct: 0.9,
+            ..sample_snapshot()
+        });
+        let latest = store.get_latest_snapshot().unwrap();
+        assert!((latest.cpu_pct - 0.9).abs() < f64::EPSILON);
+    }
+}
diff --git a/libs/mofa-metrics/src/types.rs b/libs/mofa-metrics/src/types.rs
new file mode 100644
index 00000000..12266426
--- /dev/null
+++ b/libs/mofa-metrics/src/types.rs
@@ -0,0 +1,74 @@
+// Core metric types for the Observatory dashboard.
+
+use serde::{Deserialize, Serialize};
+use std::time::{SystemTime, UNIX_EPOCH};
+
+// Current Unix time in ms
+pub fn unix_ms() -> u64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .unwrap_or_default()
+        .as_millis() as u64
+}
+
+// Node lifecycle state
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "lowercase")]
+pub enum AgentState {
+    Offline,
+    Idle,
+    Active,
+    Error,
+}
+
+impl Default for AgentState {
+    fn default() -> Self {
+        Self::Offline
+    }
+}
+
+// Single node status
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AgentStatus {
+    pub id: String,
+    pub name: String,
+    pub status: AgentState,
+    pub last_seen_ms: u64,
+}
+
+// Per stage timestamps for one ASR, LLM, TTS pipeline run
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct PipelineTrace {
+    pub asr_start_ms: u64,
+    pub asr_end_ms: u64,
+    pub llm_start_ms: u64,
+    pub llm_end_ms: u64,
+    pub tts_start_ms: u64,
+    pub tts_end_ms: u64,
+    // LLM tokens/sec (0.0 if unknown)
+    pub tokens_per_sec: f64,
+}
+
+// System metrics snapshot normalized to 0 to 1
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct SystemSnapshot {
+    // CPU
+    pub cpu_pct: f64,
+    // Memory
+    pub memory_pct: f64,
+    // GPU
+    pub gpu_pct: f64,
+    pub pipeline_latency_p50_ms: f64,
+    // Uptime
+    pub uptime_secs: u64,
+    pub timestamp_ms: u64,
+}
+
+// WebSocket broadcast event
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(tag = "type", content = "data")]
+pub enum MetricEvent {
+    AgentStatusChanged(AgentStatus),
+    PipelineCompleted(PipelineTrace),
+    SystemSnapshot(SystemSnapshot),
+}